Sol linux cmg-t_1_1.pptx

CMG-T 2010

CMG-T 2010: Unix/Linux Quick-Start

Bob Sneed, EPiC Performance Associates for CMG 2010, December 9, 2010

V1.1 - December 10, 2010

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CMG-T 2010

Preliminaries

•  Disclaimers

•  About the authors –  Adrian Cockcroft –  Bob Sneed

•  An overview of the three sessions

•  NOTE: These colored-background slides are intended to ease navigation within this slide deck

Unix/Linux Quick Start Slide 2

CMG-T 2010

Disclaimers

Opinions and views expressed herein are those of the authors. (The factual bits are mostly Adrian's.)

Bob is not a doctor - and does not even play one on TV. Oops! Bob is not with Intellimagic; it’s an error in the program. There is no warranty, expressed or implied, in the quality of the

information herein, or its fitness for any given purpose. If you goof up applying this stuff and have a bad outcome or

destroy a bunch of data – it's entirely your own fault. These CMG-T materials do not refer to and are not endorsed by the authors’ current or past employers. They are based on the

authors’ career experiences. Bob can’t speak to all of Adrian's slides quite as well as he does.

Batteries not included. Your mileage may vary (YMMV).


CMG-T 2010

This CMG-T content is primarily based on Adrian Cockcroft's 2009 materials …


CMG-T 2010

Adrian Cockcroft •  Where's Adrian?

–  Netflix 2007-present; Director of Engineering, Cloud Architectures –  CMG 2007 Michelson Award Winner for lifetime contribution to

computer measurement; http://perfcap.blogspot.com/2007/12/cmg07-and-a-michelson-award.html

–  eBay Research Labs 2004-2007; Distinguished Engineer –  Sun Microsystems 1988-2004; Distinguished Engineer

•  Adrian’s recent conference interests –  QCon and Velocity

•  Adrian’s books –  “Sun Performance and Tuning”, Prentice Hall, 1994, 1998 (2nd Ed) –  “Resource Management”, Prentice Hall, 2000 –  “Capacity Planning for Internet Services”, Prentice Hall, 2001

•  Adrian’s online presence –  Slides: http://www.slideshare.net/adrianco –  Blog: http://perfcap.blogspot.com/


CMG-T 2010

Bob Sneed •  About Bob

–  EPiC Performance Associates, 2009-present; Owner & Principal, Independent Consultant

–  Sun Microsystems,1997-2009; Sr. Staff Engineer, variously worked in Sun Competency Centers, Performance and Availability Engineering Group (PAE), and the Systems Quality Office (SQO)

•  Papers and presentations by Bob … –  “Sun/Oracle Best Practices”, Sun Blueprint, January 2001 –  “Oracle I/O; Supply and Demand”, Sun User's Performance Group

(SUPerG), 2001 –  “Performance Forensics”, Sun Blueprint, December 2003 (previously a

CMG 2002 paper) –  “I/O Microbenchmarking with Oracle in Mind”, Hotsos Symposium, 2006 –  “Capacity; It's Not All About U!”, Hotsos Symposium, 2008“Best Practices

for Optimal Configuration of Oracle Databases on Sun Hardware”, (with co-author; Allan Packer), Oracle Open World, 2009

–  “CPU QoS”, Southern Area CMG, 2010 & Hotsos Symposium 2010 –  Coming March 2011; “Brute-Force Parallelism”


CMG-T 2010

Overview

•  Session 1 is an introduction to (or review of) key principles and terminology for performance and capacity planning. This discussion will highlight many common high-level strategic errors that can lead to under- or over-provisioning or disappointing results despite adequate provisioning.

•  Session 2 will survey the data sources and tools available for traditional resource-oriented analysis (network, CPU, memory, storage), plus the tools available for understanding kernel, hardware, and per-thread program performance. Pointers will be given to some major commercial and open-source tools for performance and capacity management. Some emphasis will be placed on Solaris features including microstate accounting and DTrace.

•  Session 3 will conclude the tool survey begun in Session 2, then survey several common errors, traps, and pitfalls. This session ends with some broad guidelines on how to manage performance and capacity in Unix and Linux environments.


CMG-T 2010

Session 1 of 3

An introduction to (or review of) key principles and terminology for performance and capacity planning. This

discussion will highlight many common high-level strategic errors that can lead to under- or over-

provisioning or disappointing results despite adequate provisioning


CMG-T 2010

Definitions


CMG-T 2010

Capacity Planning Definitions •  Capacity

–  Resource utilization and headroom

•  Planning –  Predicting future needs by analyzing historical data and

modelling future scenarios

•  Performance Monitoring –  Collecting and reporting on performance data

•  Unix/Linux (apologies to users of OSX, HP-UX, AIX etc.) –  Emphasis on Solaris and Linux –  Much of the discussion is independent of the OS


CMG-T 2010

Measurement Terms and Definitions

•  Bandwidth - gross work per unit time [unattainable] •  Throughput - net work per unit time •  Peak throughput - at maximum acceptable response time •  Utilization - busy time relative to elapsed time [can be misleading] •  Queue length - number of requests waiting •  Service time - time to process a unit of work after waiting •  Response time - time to complete a unit of work including waiting •  Key Performance Indicator (KPI) – a measurement you have

decided to watch because it has some business value •  Laws – constraints which physics and math place on reality


CMG-T 2010

Service Level Agreements (SLA) •  Behavioral goals for the system in terms of KPIs

– NOTE: With or without contracted SLAs, the industry's universal KPI tends to be “call center traffic” or “rate of complaints”

•  Response time target – Rule of thumb: Estimate 95th percentile response time as three

times mean response time –  e.g. if SLA says 1 second response, measured average should

be less than 333ms

•  Utilization Target (a proxy for Response Time) –  Specified as a minimum and maximum – Minimum utilization target to keep costs down – Maximum utilization target for good response times and capacity

headroom for future workload fluctuations


CMG-T 2010

Capacity Planning Requirements

•  We care about CPU, Memory, Network and Disk resources, and Application response times

•  We need to know how much of each resource we are using now, and will use in the future

•  We need to know how much headroom we have to handle higher loads

•  We want to understand how headroom varies, and how it relates to application response times and throughput

•  The application workload must be characterized so we can understand and manage system behaviours

•  We want to be able to find the bottleneck in an under-performing system


CMG-T 2010

Laws


CMG-T 2010

Ignorance of The Law is no excuse!

•  Physics –  The speed of light – Moore's Law

•  Management – Murphy's Law –  Parkinson's Law

•  Performance and Capacity –  Amdahl's Law –  Little's Law


CMG-T 2010

The Speed of Light; Deal with it!


SPEED LIMIT

186,000 Miles Per Second

It’s not just a Good Idea!

It’s the Law!

CMG-T 2010

Physics Laws (Well, sort-of …)

•  The speed of light – Nothing can go faster; 186,000 miles/second –  “A foot is a nanosecond” –  A thousand miles is (1000/186000=) 5.4 ms, plus routing and

handling delays, in the case of digital traffic

•  Moore's Law –  From Wikipedia: “Moore's law describes a long-term trend in the

history of computing hardware. The number of transistors that can be placed inexpensively on an integrated circuit has doubled approximately every two years.[1] The trend has continued for more than half a century and is not expected to stop until 2015 or later.[2]”

– NOTE: This speaks only of circuit density, not speed. – CORRELARY: This ride is coming to an end?


CMG-T 2010

Management Laws

•  Parkinson's Law – Often stated simply as; “Work expands to fill the time available.” – Corollary: “Software bloat occurs in direct proportion to gains

from Moore's Law.” – Corollary: “Disk retention strategies vary in direct proportion to

increasing storage density.” – Corollary: “Performance optimization has no limits unless you set

them.” (Bob just made that up.)

•  Murphy's Law – Often stated simply as; “Anything that can go wrong will go

wrong; and at the most inopportune time.” –  This is what Capacity Planning aims to prevent.


CMG-T 2010

Performance and Capacity Laws Must-know!

•  Little’s Law –  Simple form: X = N/R, where X is throughput, N is degree of

concurrency, and R is response time

•  Little’s Law is crucial to spotting serialization (N=1) or determining other values of N – Q1: With 1 KB I/O size and 0.5 ms response time for reads

what is the throughput for a single I/O-bound stream? –  A1: N/R = 1 KB / 0.0005 = 2000 KB/sec = (2000/1024) or 1.95

MB/sec – Q2: What degree of concurrency would be required to attain 20

MB/sec at 0.5 ms response time and 1 KB I/O size? –  A2: N = X*R, so 20*1024*0.0005 = 10.24 (Shucks! We need

an integer N, so make that 11.)


CMG-T 2010

Performance and Capacity Laws Must-know! •  Amdahl’s Law

–  From Wikipedia: “The speedup of a program using multiple processors in parallel computing is limited by the time needed for the sequential fraction [serial portion] of the program.”

•  Things that are serialized or slow relative to CPU speed –  I/O; network or storage –  Locking; exclusive access to some data structure –  Dispatching; handling out work –  “Take a number”; sequence generation

•  A simple case of Amdahl’s Law with N=1 … –  If a process’ response time is 1 second, including all disk accesses,

network delays, and contention – and only 10% of the time is CPU – then an infinitely-fast CPU will only improve the response time to 900 ms.

–  Improving a system element only pays in proportion to the ratio of that element in total response time.


CMG-T 2010

Ignorance of The Law is no excuse!


CMG-T 2010

Workloads


CMG-T 2010

“Workload Characterization” An overloaded term! •  Homogeneous workloads

–  Generally easy to characterize and model –  Homogeneity is one justification for “tiering” solution architectures

•  System response to hosted workload(s) –  Some performance engineers view the system from the inside-out; their

metrics focus is on how the hardware, OS, and peripherals are stressed at a low level

•  Heterogeneous workloads –  These are the norm on large or complex systems –  See, e.g. Ron Kaminski's various CMG contributions

•  Circumstantial workloads –  e.g. failover processing and post-failover operations often escape

characterization, leading to in-service surprises


CMG-T 2010

Workload Characteristics: One by One Constant Workloads •  e.g. Numerical computation, compute intensive batch

•  Trivial to model, utilization and duration define the work


CMG-T 2010

Simple Random Arrivals •  Random arrival of transactions with fixed mean service

time –  Little’s Law: QueueLength = Throughput * Response –  Utilization Law: Utilization = Throughput * ServiceTime

•  Complex models are often reduced to this model –  By averaging over longer time periods since the formulas only

work if you have stable averages –  By wishful thinking (i.e. how to fool yourself)

•  e.g. Unix Load Average is actually CPU Queue Length –  Throughput up a little, load average up a lot = slow system –  So load average is a proxy metric for response time –  High load average per CPU implies slow response times


CMG-T 2010

Mixed random arrivals of transactions with stable mean service times

•  Think of the grocery store checkout analogy –  Trolleys full of shopping vs. baskets full of shopping –  Baskets are quick to service, but get stuck behind trolleys –  Relative mixture of transaction types starts to matter

•  Many transactional systems handle a mixture –  Databases, web services

•  Consider separating fast and slow transactions –  So that we have a “10 items or less” line just for baskets –  Separate pools of servers for different services –  Don’t mix OLTP with DSS queries in databases

•  Performance is often thread-limited –  Thread limit and slow transactions constrains maximum

throughput –  Throughput = Queue / ResponseTime

•  Model using analytical solvers like PDQ


CMG-T 2010

Load dependent servers – non-stable mean service times

•  Mean service time increases at high throughput –  Due to non-scalable algorithms, lock contention, thrashing –  System runs out of memory and starts paging or frequent GC

•  Many systems have “tipping points” –  Hysteresis means they don’t come back when load drops –  This is why you have to kill catatonic systems –  Some systems actually degrade gracefully under load

•  Model using simulation tools like Hyperformix, Opnet –  Behaviour is non-linear and hard to model –  Practical option is to avoid tipping points –  Best designs shed load to be stable at the limit


CMG-T 2010

Self-similar / fractal workloads – bursty rather than random

•  Self-similar –  Looks “random” at close up, stays “random” as you zoom out –  Work arrives in bursts, transactions aren’t independent –  Bursts cluster together in super-bursts, etc.

•  Network packet streams tend to be fractal •  Common in practice, too hard to model

–  Probably the most common reason why your model is wrong!


CMG-T 2010

State Dependent Services

•  Personalized services that store user history –  Transactions for new users are quick –  Transactions for users with lots of state/history are slower –  As user base builds state and ages you get into lots of trouble…

•  Social Networks, Recommendation Services –  Facebook, Flickr, Netflix, Pandora, Twitter etc.

•  “Abandon hope all ye who enter here” –  Not tractable to model, repeatable tests are tricky –  Long fat tail response time distribution and timeouts –  Excessively long service times for some users –  Solutions: careful algorithm design, lots of caching


CMG-T 2010

Workload Modelling Survivalism

•  Simplify the workload algorithms –  move from hard or impossible to simpler models –  use caching and pre-compute to get constant service times

•  Stand further away –  averaging is your friend – gets rid of complex fluctuations

•  Minimalist Models –  most models are far too complex – the classic beginners error… –  the art of modelling is to only model what really matters

•  Don’t model details you don’t use –  model peak hour of the week, not day to day fluctuations –  e.g. “Will the web site survive next Sunday night?”


CMG-T 2010

Contrarian Perspective on Workloads

•  Classical breakdown, e.g. for CPU –  %usr –  %sys

•  A more-practical breakdown –  Work; what the system was bought to do – categorized by its

importance to the business –  Overhead; memory management, I/O and network stacks, lock

management, context switches, migrations –  Opportunistic usage; over-achievers (including screen-savers, low-

priority workload elements, and high-priority workload elements) –  Waste; bugs, inefficient code, absence of Best Practices

•  Stovepiped organizations that feed only classical data to the Capacity Planners will predictably over-provision –  Gains attainable from improved efficiency, performance discipline, and

teamwork represent “latent capacity”; it’s often huge


CMG-T 2010

Strategies


CMG-T 2010

Performance and Capacity Strategies

1. Empirical Methods (Great! Only expensive if you do it! Benchmarks, stress testing, test-to-scale, test-to-fail – with known Best Practices & basic performance analysis and tuning

2. Modeling (Highly recommended, moderate cost) Using tools such as TeamQuest Model (TQM), BMC Perform/Predict, Hy-Performix, Gunther's PDQ or other application of proper science and math

3. Expert Opinions (Recommended minimum, cheapest Listening to the right experts for Best Practices, analysis and tuning methods, and sizing. The hazard with opinions is that there are so many of them!

4. Guesswork (The Norm) Straight-line extrapolations, naïve use of reference benchmarks, massive over-provisioning, misdirected or uncontrolled testing, blind luck

5. Opportunism (Commonplace) Spend the available budget


CMG-T 2010

Best Practices

•  Absent Best Practices … –  Performance, stability, capacity, or predictability may all suffer –  Capacity planners may end up scaling-up groww inefficiency –  Data from from the system will not directly indicate the deviation –  One is prone to “re-inventing the wheel” –  It’s like having Yellow Fever versus getting the innoculation

•  Best Practices are … –  Repeatable, time-proven practices –  Steps to take as a matter of routine –  Possibly highly-localized and application-specific –  Goal-oriented; eg: simplicity, performance, cost

•  Best Practices are not … –  A lab result or single practitioner’s experience, extrapolated to the

general case –  A guarantee of automatic success in all things


CMG-T 2010

A Best Practice Example

•  A Best Practice for performance, consistency, and scalability of storage for Oracle databases is to use a solution with these characteristics: –  Unbuffered; no stress on OS buffer memory management –  Concurrent; no single-writer lock or similar bottlenecks –  Stable data placement; facilitates high-bandwidth reads

•  Many compliant options exist, including –  UFS with direct I/O; QFS with samaio; RAW; Oracle Automated

Storage Management (ASM); VxFS with QIO, ODM, or cio+direct

•  See also http://blogs.sun.com/bobs/entry/one_i_o_two_i –  I’ve added “stable data placement” to the criteria since that blog entry

to reflect experiences seen with WAFL-type filesystems –  There is a vast amount of energy that gets spent annually learning

these things the hard way or trying to work-around them


CMG-T 2010

Session 2 of 3

A survey the data sources and tools available for traditional resource-oriented analysis (network, CPU,

memory, storage), plus the tools available for understanding kernel, hardware, and per-thread program

performance. Pointers will be given to some major commercial and open-source tools for performance and capacity management. Some emphasis will be placed on Solaris features including microstate accounting and

DTrace.


CMG-T 2010

Metrics


CMG-T 2010

Measurement Data Interfaces •  Several generic raw access methods

–  Read the kernel directly –  Structured system data –  Process data –  Network data –  Accounting data –  Application data

•  Command based data interfaces –  Scrape data from vmstat, iostat, netstat, sar, ps –  Higher overhead, lower resolution, missing metrics

•  Data available is generally platform- and release-specific •  Extremely valuable, but not discussed here …

–  Application-level instrumentation; e.g. Oracle RDBMS –  WAN, SAN, and LAN “sniffers”; sample data “outside the box”


CMG-T 2010

Reading kernel memory - kvm

•  The only way to get data in very old Unix variants

•  Use kernel namelist symbol table and open /dev/kmem

•  Solaris wraps up interface in kvm library

•  Advantages –  Still the only way to get at some kinds of data –  Low overhead, fast bulk data capture

•  Disadvantages –  Too much intimate implementation detail exposed –  No locking protection to ensure consistent data –  Highly non-portable, unstable over releases and patches –  Tools break when kernel moves between 32 and 64bit address

support


CMG-T 2010

Structured Kernel Statistics - kstat

•  Solaris 2 introduced kstat and extended usage in each release •  Used by Solaris 2 vmstat, iostat, sar, network interface stats, etc.

•  Advantages –  The recommended and supported Solaris metric access API –  Does not require setuid root commands to access for reads –  Individual named metrics stable over releases –  Consistent data using locking, but low overhead –  Unchanged when kernel moves to 64bit address support –  Extensible to add metrics without breaking existing code

•  Disadvantages –  Somewhat complex hierarchical kstat_chain structure –  State changes (device online/offline) cause kstat_chain

rebuild


CMG-T 2010

Kernel Tracing - TNF, prex, ktrace

•  Solaris, Linux, Windows and other Unixes have similar features –  Solaris has TNF probes and prex command to control them –  User level probe library for hires tracepoints allows

instrumentation of multithreaded applications –  Kernel level probes allow disk I/O and scheduler tracing

•  Advantages –  Low overhead, microsecond resolution –  I/O trace capability is extremely useful

•  Disadvantages –  Too much data to process with simple tracing capabilities –  Trace buffer can overflow or cause locking issues


CMG-T 2010

DTrace – Dynamic Tracing •  One of the most exciting new features in Solaris 10, rave reviews

–  Also in Apple's OS X 10.5; man -k dtrace, plus “Instruments” GUI

•  Advantages –  No overhead when it is not in use –  Low overhead probes can be put anywhere/everywhere –  Trace data is correlated and filtered at source; get exactly the data

you want; very sophisticated data providers included –  Bundled, supported, designed to be safe for production systems –  Stable foundation for many tools; system tools, scripts, and GUIs

•  Disadvantages –  Not on Linux yet –  Excessive DTrace probes can cause high systemic overhead (which

is only a problem is it occurs by accident); proven scripts avoid this –  Yet another (awk-like) scripting language to learn; pre-packaged

scripts can avoid this, also


CMG-T 2010

DTrace – Dynamic Tracing •  References

–  Book: "Solaris Performance and Tools" by Richard McDougall, Jim Mauro, and Brendan Gregg, Prentice-Hall, 2006

–  Guide: “How to Use Oracle® Solaris DTrace from Oracle Solaris and OpenSolaris System” @ http://developers.sun.com/solaris/docs/o-s-dtrace-htg.pdf

–  Treasure trove: Brendan Gregg's DTrace Toolkit @ http://www.brendangregg.com/dtrace.html


CMG-T 2010

Hardware counters •  Most modern CPUs and systems have hardware counters; tools to access

these counters are quite varied … –  Solaris cpustat for X86 and UltraSPARC pipeline and cache counters, corestat for

multi-core systems; busstat for server backplanes and I/O buses –  Solaris Intel Trace Collector, Vampir for Linux –  AMD EMON; only under license

•  Advantages –  See what is really happening; more accurate than kernel stats –  Cache usage useful for tuning code algorithms –  Pipeline usage useful for HPC tuning for megaflops –  Some VA/PA/TLB memory-management details only observable via counters –  Backplane and memory bank usage useful for database servers

•  Disadvantages –  Raw data is confusing; requires post-processing scripts –  Privilege needed for access; not sharable to hosted virtual domains –  Lots of propeller-headed architectural background info needed –  Most tools focus on developer code tuning


CMG-T 2010

Configuration information

•  System configuration data comes from too many sources! –  Solaris device tree displayed by prtconf and prtdiag –  Solaris 8 adds dynamic configuration notification device picld –  SCSI device info using iostat -E in Solaris –  Logical volume info from product specific vxprint and metastat –  Hardware RAID info from product specific tools –  Critical storage config info must be accessed over ethernet… –  Linux device tree in /proc is a bit easier to navigate

•  It is very hard to combine all this data!

•  DMTF CIM objects try to address this, but no-one seems to use them…

•  Free tool - Config Engine: http://www.cfengine.org


CMG-T 2010

Application instrumentation Examples •  Oracle V$ Tables – detailed metrics used by many tools •  Apache logging for web services

•  ARM standard instrumentation

•  Custom do-it-yourself and log file scraping

•  Advantages –  Focussed application specific information –  Business metrics are needed to do real capacity planning

•  Disadvantages –  No common access methods –  ARM is a collection interface only, vendor specific tools, data –  Very few applications are instrumented, even fewer have support

from performance tools vendors


CMG-T 2010

Kernel values, tunables and defaults •  There is often far too much emphasis on kernel tweaks

–  There really are few “magic bullet” tunables –  It rarely makes a significant difference

•  Fix the system configuration or tune the application instead!

•  Very few adjustable components –  “No user serviceable parts inside” –  But Unix has so much history people think it is like a 70’s car –  Solaris really is dynamic, adaptive and self-tuning –  Most other “traditional Unix” tunables are just advisory limits –  Tweaks may be workarounds for bugs/problems –  Patch or OS release removes the problem - remove the tweak

Solaris Tunable Parameters Reference Manual (if you must…) –  http://docs.sun.com/app/docs/doc/817-0404


CMG-T 2010

Process-based data in /proc

•  /proc filesystem is a common foundation –  Used by ps, proctool and debuggers, pea.se, proc(1) tools on Solaris –  Solaris and Linux both have /proc/pid/metric hierarchy –  Linux also includes system information in /proc rather than kstat

•  Advantages –  The recommended and supported process access API –  Metric data structures reasonably stable over releases –  Consistent data using locking –  Solaris microstate data provides accurate process state timers

•  Disadvantages –  High overhead for open/read/close of every process on busy

systems –  Linux reports data as formatted ASCII text, Solaris uses binary

structures that require tools for formatting


CMG-T 2010

Network protocol data •  Based on a streams module interface in Solaris •  Solaris 2 ndd interface used to configure protocols and interfaces •  Solaris 2 mib interface used by netstat -s and snmpd to get TCP

stats etc. •  Advantages

–  Individual named metrics reasonably stable over releases –  Consistent data using locking –  Extensible to add metrics without breaking existing code –  Solaris ndd can retune TCP online without reboot –  System data is often also made available via SNMP protocol

•  Disadvantages –  Underlying API is not supported, SNMP access is preferred


CMG-T 2010

Tracing and profiling

•  Tracing Tools –  truss - shows system calls made by a process –  sotruss / apitrace - shows shared library calls –  prex - controls TNF tracing for user and kernel code –  snoop/tcpdump – network traces for analysis with wireshark

•  Profiling Tools –  Compiler profile feedback using -xprofile=collect and use –  Sampled profile relink using -p and prof/gprof –  Function call tree profile recompile using -pg and gprof –  Shared library call profiling setenv LD_PROFILE and gprof

•  Accurate CPU timing for process using /usr/proc/bin/ptime •  Microstate process information using pea.se and pw.se 10:40:16 name lwmx pid ppid uid usr% sys% wait% chld% size rss pf nis_cachemgr 5 176 1 0 1.40 0.19 0.00 0.00 16320 11584 0.0 jre 1 17255 3184 5743 11.80 0.19 0.00 0.00 178112 110336 0.0 sendmail 1 16751 1 0 1.01 0.43 0.00 0.43 18624 16384 0.0 se.sparc.5.6 1 16741 1186 9506 5.90 0.47 0.00 0.00 16320 14976 0.0 imapd 1 16366 198 5710 6.88 1.09 1.02 0.00 34048 29888 0.1 dtmail 10 16364 9070 5710 0.75 1.12 0.00 0.00 102144 94400 0.0


CMG-T 2010

Free Tools

(See Separate Slide Deck) http://www.slideshare.net/adrianco


CMG-T 2010

Headroom? What’s the matter with U?


CMG-T 2010

What would you say if you were asked:

How busy is that system?

A: “I have no idea.”

A: “42%”

A: “Why do you want to know?”

A: “I’m sorry, but I’m afraid that you don’t understand your question.”


CMG-T 2010

Utilization •  It looks simple enough …

–  Utilization is the proportion of busy time –  Always defined over a time interval –  Instantaneously, it’s binary; 100% or 0% –  Let’s run with this for a while, then circle back to the issues …


usr+sys CPU for Peak Period

0102030405060708090100

Time

CP

U %

Utilization

OnCPU Scheduling for Each CPU

0

0.56

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Microseconds

On

CP

U a

nd

M

ean

CP

U U

til

CMG-T 2010

Headroom •  Headroom relates to available usable resources

–  Total Capacity minus Peak Utilization and Margin –  Applies to CPU, RAM, Net, Disk and OS –  “Usable” is the rub; idle resources may not be actually

usable due to software bottlenecks, such as locking or limited concurrency


usr+sys CPU for Peak Period

0102030405060708090100

Time

CP

U %

Headroom

Utilization

Margin

CMG-T 2010

Headroom Estimation

•  CPU Capacity – Relatively easy to figure out for well-behaved, homogeneous,

steady-state workloads –  “Over-achievers”, bad tuning, and common Best Practice

deviations inflate perception of required capacity

•  Network Usage – Use bytes not packets/s

•  Memory Capacity –  Tricky - easier in Solaris 8

•  Disk Capacity – Can be very complex –  A complex gamut of software layers may reside between the

application and its disk


CMG-T 2010

Response Time

•  Response Time = Queue time + Service time

•  The Usual Assumptions … –  Steady state averages –  Random arrivals –  Constant service time –  M servers processing the same queue

•  Approximations –  Queue length = Throughput * Response Time (Little's Law)

–  Utilization = Throughput * Service Time (Utilization law) –  Response Time = Service Time / (1 - UtilizationM)


CMG-T 2010

Response Time Curves

•  The traditional view of Utilization as a proxy for response time •  Systems with many CPUs can run at higher utilization levels, but degrade

more rapidly when they run out of capacity •  Headroom margin should be set according to a response time target


Response Time Curves

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

0 10 20 30 40 50 60 70 80 90 100Total System Utilization %

Res

pon

se T

ime

Incr

ease

Fac

tor

One CPUTwo CPUsFour CPUsEight CPUs16 CPUs32 CPUs64 CPUs

Headroom margin

R = S / (1 - (U%)m)

CMG-T 2010

So what's the problem with Utilization?

•  Unsafe assumptions! –  Modern systems are complex, adaptive, highly non-linear, and are often

virtualized or include shared components

•  Random arrivals? –  Bursty traffic with long tail arrival rate distribution

•  Constant service time? –  Variable clock rate CPUs, inverse load dependent service time –  Complex transactions, request and response dependent

•  M servers processing the same queue? –  Virtual servers with varying non-integral concurrency –  Non-identical servers or CPUs, Hyperthreading, Multicore, NUMA

•  Measurement Errors? –  Mechanisms with built in bias, e.g. sampling from the scheduler clock –  Platform and release specific systemic changes in accounting of

interrupt time


CMG-T 2010

Variable Clock Rate CPUs

•  Laptop and other low power devices do this all the time –  Watch CPU usage of a video application and toggle mains/battery power

•  Server CPU Power Optimization - AMD PowerNow!™ –  AMD Opteron server CPU detects overall utilization and reduces clock

rate –  Actual speeds vary, but for example could reduce from 2.6GHz to

1.2GHz –  Changes are not understood or reported by operating system metrics –  Speed changes can occur every few milliseconds (thermal shock issues) –  Dual core speed varies per socket, Quad core varies per core –  Quad core can dynamically stop entire cores to save power –  Note: Older and "low power" Opterons in blades use fixed clock rate

•  Possible scenario: –  You estimate 20% utilization at 2.6GHz –  You see 45% reported in practice (at 1.2GHz) –  Load doubles, reported utilization drops to 40% (at 2.6GHz) –  Actual mapping of utilization to clock rate is unknown at this point


CMG-T 2010

Virtual Machine Monitors

•  VMware, Xen, IBM LPARs etc. –  Non-integral and non-constant fractions of a machine –  Naive operating systems and applications don't expect this behavior –  However, lots of recent tools development from vendors

•  Average CPU count must be reported for each measurement interval

•  VMM overhead varies, application scaling characteristics may be affected


CMG-T 2010

Threaded CPU Pipelines

•  CPU microarchitecture optimizations –  Extra register sets working with one execution pipeline –  When the CPU stalls on a memory read, it switches registers/threads –  Operating system sees multiple schedulable entities (CPUs)

•  Intel Hyperthreading –  Each CPU core has an extra thread to use spare cycles –  Typical benefit is 20%, so total capacity is 1.2 CPUs –  I.e. Second thread much slower when first thread is busy –  Hyperthreading aware optimizations in recent operating systems

•  Sun “CoolThreads” –  "Niagara" SPARC CPU has eight cores, one shared floating point unit –  Each CPU core has four threads, but each core is a very simple design –  Behaves like 32 slow CPUs for integer, snail-like uniprocessor for FP –  Overall throughput is very high, performance per watt is exceptional –  Niagara 2 has dedicated FPU and 8 threads per core (total 64 threads) –  Each generation varies in low-level architectural details


CMG-T 2010

Measurement Errors

•  Mechanisms with built in bias –  e.g. sampling from the scheduler clock underestimates CPU usage

–  Solaris 9 and before, Linux, AIX, HP-UX “sampled CPU time”

–  Solaris 10 and HP-UX “measured CPU time” far more accurate

–  Solaris microstate process accounting always accurate but in Solaris 10 microstates are also used to generate system-wide CPU

•  Accounting for interrupt time –  Platform and release specific systemic changes

–  Solaris 8 - sampled interrupt time spread over usr/sys/idle

–  Solaris 9 - sampled interrupt time accumulated into sys only

–  Solaris 10 – measured interrupt time spread over usr/sys/idle

–  Solaris 10 Update 1 – measured interrupt time in sys only


CMG-T 2010

CPU time measurements

•  Biased sample CPU measurements –  See 1998 Paper "Unix CPU Time Measurement Errors" –  Microstate measurements are accurate, but are platform and tool specific.

Sampled metrics are more inaccurate at low utilization

•  CPU time is sampled by the 100Hz clock interrupt –  sampling theory says this is accurate for an unbiased sample –  the sample is very biased, as the clock also schedules the CPU –  daemons that wakeup on the clock timer can hide in the gaps –  problem gets worse as the CPU gets faster

•  Increase clock interrupt rate? (Solaris) –  set hires_tick=1 sets rate to 1000Hz, good for realtime wakeups –  harder to hide CPU usage, but slightly higher overhead

•  Use measured CPU time at per-process level –  microstate accounting takes timestamp on each state change –  very accurate and also provides extra information –  still doesn’t allow for interrupt overhead –  Prstat -m and the pea.se command uses this accurate measurement


CMG-T 2010

More CPU Measurement Issues

•  Load average differences –  Just includes CPU queue (Solaris) –  Includes CPU and Disk (Linux) – which is a broken metric

•  Wait for I/O (%wio) is a misleading statistic altogether –  Metric removed in Solaris 10 – always zero –  Ignore it in all other Unix/Linux releases; add it to %idle –  There is no universal “propensity to compute” for a thread

blocked on I/O; who knows how much %cpu it might use when it wakes up?


CMG-T 2010

How to plot Headroom

•  Measure and report absolute CPU power if you can get it …

•  Plot shows headroom in blue, margin in red, total power tracking day/night workload variation, plotted as mean + two standard deviations.


CMG-T 2010

“Cockcroft Headroom Plot”

•  Scatter plot of response time (ms) vs. Throughput (KB) from iostat metrics

•  Histograms on axes

•  Throughput time series plot

•  Shows distributions and shape of response time

•  Fits throughput weighted inverse gaussian curve

•  Coded using "R" statistics package

•  Blogged development at http://perfcap.blogspot.com/search?q=chp


CMG-T 2010

How busy is that system again?

•  Check your assumptions …

•  Record and plot absolute capacity for each measurement interval

•  Plot response time as a function of throughput, not just utilization

•  SOA response characteristics are complicated … •  More detailed discussion in CMG06 Paper and blog entries

–  “Utilization is Virtually Useless as a Metric” - Adrian Cockcroft - CMG06

http://perfcap.blogspot.com/search?q=utilization

http://perfcap.blogspot.com/search?q=chp


CMG-T 2010

CPU


CMG-T 2010

CPU Capacity Measurements

•  CPU Capacity is defined by CPU type and clock rate, or a benchmark rating like SPECrateInt2000

•  CPU throughput - CPU scheduler transaction rate –  measured as the number of voluntary context switches

•  CPU Queue length –  CPU load average gives an approximation via a time

decayed average of number of jobs running and ready to run •  CPU response time

–  Solaris microstate accounting measures scheduling delay •  CPU utilization

–  Defined as busy time divided by elapsed time for each CPU –  Badly distorted and undermined by virtualization……


CMG-T 2010

Controlling and CPUs in Solaris

•  psrinfo - show CPU status and clock rate •  Corestat - show internal behavior of multi-core CPUs •  psradm - enable/disable CPUs •  pbind - bind a process to a CPU •  psrset - create sets of CPUs to partition a system

–  At least one CPU must remain in the default set, to run kernel services like NFS threads

–  All CPUs still take interrupts from their assigned sources –  Processes can be bound to sets

•  mpstat shows per-CPU counters (per set in Solaris 9) CPU minf mjf xcal intr ithr csw icsw migr smtx srw syscl usr sys wt idl 0 45 1 0 232 0 780 234 106 201 0 950 72 28 0 0 1 29 1 0 243 0 810 243 115 186 0 1045 69 31 0 0 2 27 1 0 235 0 827 243 110 199 0 1000 75 25 0 0 3 26 0 0 217 0 794 227 120 189 0 925 70 30 0 0 4 9 0 0 234 92 403 94 84 1157 0 625 66 34 0 0


CMG-T 2010

Monitoring CPU mutex lock statistics

•  To fix mutex contention change the application workload or upgrade to a newer OS release

•  Locking strategies are too complex to be patched •  lockstat Command

–  very powerful and easy to use –  Solaris 8 extends lockstat to include kernel CPU time profiling –  dynamically changes all locks to be instrumented –  displays lots of useful data about which locks are contending

# lockstat sleep 5 Adaptive mutex spin: 3318 events Count indv cuml rcnt spin Lock Caller ------------------------------------------------------------------------------- 601 18% 18% 1.00 1 flock_lock cleanlocks+0x10 302 9% 27% 1.00 7 0xf597aab0 dev_get_dev_info+0x4c 251 8% 35% 1.00 1 0xf597aab0 mod_rele_dev_by_major+0x2c 245 7% 42% 1.00 3 0xf597aab0 cdev_size+0x74 160 5% 47% 1.00 7 0xf5b3c738 ddi_prop_search_common+0x50


CMG-T 2010

Network


CMG-T 2010

Network interface and NFS metrics

•  Network interface throughput counters from kstat on Solaris –  rbytes, obytes — read and output byte counts –  multircv, multixmt — multicast byte counts –  brdcstrcv, brdcstxmt — broadcast byte counts –  norcvbuf, noxmtbuf — buffer allocation failure counts

•  Linux netstat shows byte throughput (Solaris doesn’t)

•  NFS Client Statistics Shown in iostat on Solaris crun% iostat -xnP extended device Statistics r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 crun:vold(pid363) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 servdist:/usr/dist 0.0 0.5 0.0 7.9 0.0 0.0 0.0 20.7 0 1 servhome:/export/home/adrianc 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 servhome:/var/mail 0.0 1.3 0.0 10.4 0.0 0.2 0.0 128.0 0 2 c0t2d0s0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c0t2d0s2


CMG-T 2010

TCP - A Simple Approach

•  Capacity and Throughput Metrics to Watch

•  Connections – Current number of established connections – New outgoing connection rate (active opens) – Outgoing connection attempt failure rate – New incoming connection rate (passive opens) –  Incoming connection attempt failure rate (resets)

•  Throughput –  Input and output byte rates –  Input and output segment rates – Output byte retransmit percentage


CMG-T 2010

Obtaining Measurements

•  Get the TCP MIB via SNMP or netstat -s

•  Standard TCP metric names: –  tcpCurrEstab: current number of established connections –  tcpActiveOpens: number of outgoing connections since boot –  tcpAttemptFails: number of outgoing failures since boot –  tcpPassiveOpens: number of incoming connections since boot –  tcpOutRsts: number of resets sent to reject connection –  tcpEstabResets: resets sent to terminate established

connections –  (tcpOutRsts - tcpEstabResets): incoming connection failures –  tcpOutDataSegs, tcpInDataSegs: data transfer in segments –  tcpRetransSegs: retransmitted segments


CMG-T 2010

Internet Server Issues

•  TCP Connections are expensive –  TCP is optimized for reliable data on long lived connections – Making a connection uses a lot more CPU than moving data – Connection setup handshake involves several round trip delays –  Each open connection consumes about 1 KB plus data buffers

•  Pending connections cause “listen queue” issues

•  Each new connection goes through a “slow start” ramp up

•  Other TCP Issues –  TCP windows can limit high latency high speed links –  Lost or delayed data causes time-outs and retransmissions


CMG-T 2010

TCP Sequence Diagram for HTTP Get


CMG-T 2010

Stalled HTTP Get and Persistent HTTP


CMG-T 2010

Memory


CMG-T 2010

Memory Capacity Measurements

•  Physical Memory Capacity Utilization and Limits –  Kernel memory, Shared Memory segment –  Executable code, stack and heap –  File system cache usage, Unused free memory

•  Virtual Memory Capacity - Paging/Swap Space –  When there is no more available swap, Unix stops working

•  Memory Throughput –  Hardware counter metrics can track CPU to Memory traffic –  Page in and page out rates

•  Memory Response Time –  Platform specific hardware memory latency makes a difference,

but hard to measure –  Time spent waiting for page-in is part of Solaris microstate

accounting


CMG-T 2010

Page Size Optimization •  Systems may support large pages for reduced overhead

–  Solaris support is more dynamic/flexible than Linux at present •  Intimate Shared Memory locks large pages in RAM

– No swap space reservation – Used for large database server Shared Global Area

•  No good metrics to track usage and fragmentation issues •  Solaris ppgsz command can set heap and stack pagesize •  SPARC Architecture

–  Base page size is 8KB, Large pages are 4MB •  Intel/AMD x86 Architectures

–  Base page size is 4KB, Large pages are 2MB


CMG-T 2010

Cache principles •  Temporal locality - “close in time”

–  If you need something frequently, keep it near you –  If you don’t use it for a while, put it back –  If you change it, save the change by putting it back

•  Spacial locality - “close in space - nearby” –  If you go to get one thing, get other stuff that is nearby –  You may save a trip by prefetching things –  You can waste bandwidth if you fetch too much you don’t use

•  Caches work well with randomness –  Randomness prevents worst case behaviour –  Deterministic patterns often cause cache busting accesses

•  Very careful cache friendly tuning can give great speedups


CMG-T 2010

The memory go round - Unix/Linux

•  Memory usage flows between subsystems

Kernel System V

Free

Process Filesystem

Head

Ta il

RAM

CacheStack andHeap

exitbrk

reclaim

pagein

pageout pageout

delete

readwritemmap

reclaim

SharedMemory

List

kernelalloc

kernelfree shmget

shm_unlink

MemoryBuffers

scanner scanner

Slide 84 Unix/Linux Quick Start

CMG-T 2010

The memory go round - Solaris 8 and Later

•  Memory usage flows between subsystems

Kernel System V

Free RAM List

ProcessFilesystem

Head

Ta ilCache

Stack andHeap

exitbrk

reclaim

pagein

pageout

deletereadwritemmap

SharedMemory

kernelalloc

kernelfree shmget

shm_unlink

MemoryBuffers

scanner


CMG-T 2010

Solaris Swap Space •  Swap is very confusing and badly instrumented! # se swap.se

ani_max 54814 ani_resv 19429 ani_free 37981 availrmem 13859 swapfs_minfree 1972 ramres 11887 swap_resv 19429 swap_alloc 16833 swap_avail 47272 swap_free 49868

Misleading data printed by swap -s

134664 K allocated + 20768 K reserved = 155432 K used, 378176 K available

Corrected labels:

134664 K allocated + 20768 K unallocated = 155432 K reserved, 378176 K available

Mislabelled sar -r 1

freeswap (really swap available) 756352 blocks

Useful swap data:

Total swap 520 M available 369 M reserved 151 M Total disk 428 M Total RAM 92 M

# swap -s

total: 134056k bytes allocated + 20800k reserved = 154856k used, 378752k available

# sar -r 1

18:40:51 freemem freeswap

18:40:52 4152 756912


CMG-T 2010

Session 3 of 3

Finish the tool survey begun in Session 2, then survey several common errors, traps, and pitfalls. This session ends with some broad guidelines on how to manage performance and capacity in Unix

and Linux environments.


CMG-T 2010

Disk


CMG-T 2010

Disk Capacity Measurements

•  Detailed metrics vary by platform

•  Easy for the simple disk cases

•  Hard for cached RAID subsystems

•  Almost Impossible for shared disk subsystems and SANs –  Another system or volume can be sharing a backend

spindle, when it gets busy your own volume can saturate, even though you did not change your own workload!


CMG-T 2010

Storage Utilization

•  Storage virtualization broke utilization metrics a long time ago

•  Host server measures busy time on a "disk" –  Simple disk, "single server" response time gets high near 100%

utilization –  Cached RAID LUN, one I/O stream can report 100% utilization, but

full capacity supports many threads of I/O since there are many disks and RAM buffering

•  New metric - "Capability Utilization" –  Adjusted to report proportion of actual capacity for current workload

mix –  Measured by tools such as Ortera Atlas (http://www.ortera.com)


CMG-T 2010

Solaris Filesystems •  ufs - standard, reliable, good for lots of small files,

–  ufs transaction logging; faster writes and recovery –  ufs direct I/O feature; especially useful with databases –  snapshot features

•  tmpfs - fastest if you have enough RAM, volatile •  NFS

–  NFS2 - safe and common, 8KB blocks, slow writes –  NFS3 - more readahead and writebehind, faster

•  default 32KB block size - fast sequential, may be slow random •  default TCP instead of UDP, more robust over WAN

–  NFS4 - adds stateful behavior •  cachefs - good for read-mostly NFS speedup •  Veritas VxFS – 3rd-party; expensive

–  Extent-based, with features for database performance and clustering •  QFS

–  Extent-based, with features for database performance and clustering –  No more investments being made there

•  ZFS – 21st century virtualized storage –  Feature-rich –  Challenging to performance-manage –  Focal point for added development


CMG-T 2010

Solaris 10 ZFS: What it doesn't have ...

•  Nice features –  No extra cost - its bundled in a free OS –  No volume manager - its built-in –  No space management - file systems use a common pool –  No long wait for newfs to finish - create a 3TB file system in a second –  No fsck - its transactional commit means its consistent on disk –  No slow writes - disk write caches are enabled and flushed reliably –  No random or small writes - all writes are large batched sequential –  No rsync - snapshots can be differenced and replicated remotely –  No silent data corruption - all data is checksummed as it is read –  No bad archives - all the data in the file system is scrubbed regularly –  No penalty for software RAID - RAID-Z has a clever optimization

(though it has limited practical applications) –  No downtime - mirroring, RAID-Z and hot spares –  No immediate maintenance - double parity disks if you need them

•  Wish-list –  No way to know how much performance headroom you have! –  No clustering support


CMG-T 2010

Solaris ZFS: Fundamental Tradeoffs

•  All physical I/O ultimately occurs in ZFS <recordsize> quanta, which defaults to 128 KB (but can be set per-pool) –  Random reads with poor locality may suffer when logical I/O size is

small relative to the physical I/O size –  Sequential reads can suffer when physical I/O size is small relative to

logical I/O size, though ZFS prefetching often effectively offsets this

•  All writes are Copy-On-Write (COW) to fresh space in the pool –  Randomly-updated data tends to become physically fragmented –  Sequential read performance can vary significantly with the degree of

physical fragmentation –  Backend prefetch algorithms are generally thwarted by fragmentation

•  All I/O is buffered and checksummed –  This increases CPU demand relative to raw or direct I/O options –  Memory management may become seriously complicated by

allocations for the Adaptive Replacement Cache (ARC) –  ZFS record checksums may be redundant with application data

protections (e.g. Oracle checksums)


CMG-T 2010

Solaris ZFS: Storage Appliances

•  Sun S7000 Storage –  Inexpensive storage solutions based on commodity components –  Spawned from Sun’s “Fishworks” team –  Downloadable simulator allows easy experimentation –  See http://www.oracle.com/us/products/servers-storage/storage/unified-storage/index.html

•  Performance Analysis & Management Features –  Storage Analytics; powerful GUI-based monitoring and analysis.

For a most unusual unusual peek at the Storage Analytics tool, see the video @ http://blogs.sun.com/brendan/entry/unusual_disk_latency

–  Configuration option for latency-sensitivity (use SSD-based ZILs) or throughput (skip the SSD-based ZILs)


CMG-T 2010

Solaris ZFS: Resources

•  Review these … –  “ZFS Evil Tuning Guide”

http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide –  “Configuring Oracle® Solaris ZFS for an Oracle Database”

http://developers.sun.com/solaris/docs/wp-oraclezfsconfig-0510_ds_ac2.pdf –  arcstat.pl Perl script

http://www.solarisinternals.com/wiki/index.php/Arcstat

•  … but don’t forget that ZFS has several fundamental tradeoffs that can be perplexing for performance and capacity management


CMG-T 2010

Linux Filesystems

•  There are a large number of options! –  http://en.wikipedia.org/wiki/Comparison_of_file_systems

•  EXT3 –  Common default for many Linux distributions –  Efficient for CPU and space, small block size –  relatively simple for reliability and recovery –  Journalling support options can improve performance –  EXT4 came out of development at the end of 2008

•  XFS –  Based on Silicon Graphics XFS, mature and reliable –  Better for large files and streaming throughput –  High Performance Computing heritage


CMG-T 2010

Disk Configurations

•  Sequential access is ~10 times faster than random –  Sequential rates are now about 50-100 MB/s per disk –  Random rates are 166 operations/sec, (250/sec at 15000rpm) –  The size of each random read should be as big as possible

•  Reads should be cached in main memory –  “The only good fast read is the one you didn’t have to do” –  Database shared memory or filesystem cache is microseconds –  Disk subsystem cache is milliseconds, plus extra CPU load –  Underlying disk is ~6ms, as its unlikely that data is in cache

•  Writes should be cached in nonvolatile storage –  Allows write cancellation and coalescing optimizations –  NVRAM inside the system - Direct access to Flash storage –  Solid State Disks based on Flash are the "Next Big Thing"


CMG-T 2010

Disk Throughput


0

2000

4000

6000

8000

10000

12000

14000

3.47222E-05 0.177118056 0.350740741 0.527824074 0.704872685 0.881944444

disk_wK/s disk_rK/s

CMG-T 2010

Max and Avg Disk Utilization (Same data)


0

10

20

30

40

50

60

70

80

90

100

3.47222E-05 0.177118056 0.350740741 0.527824074 0.704872685 0.881944444

disk_max% disk_avg%

CMG-T 2010

Data from iostat •  What can we see here? extended disk statistics !disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b !sd7 0.1 1.7 0.1 13.3 0.0 0.2 109.8 0 1 !sd15 534.2 17.5 1320.4 35.0 0.0 0.3 0.6 0 26 !sd45 291.9 23.0 603.2 49.8 0.0 0.2 0.6 0 15 !sd60 3.1 0.0 25.3 0.0 0.0 0.0 7.8 0 2 !sd61 3.3 0.0 26.4 0.0 0.0 0.0 7.6 0 2 !sd62 3.2 0.0 26.1 0.0 0.0 0.0 8.1 0 3 !sd63 3.8 0.0 30.1 0.0 0.0 0.0 7.2 0 3 !sd64 3.6 0.0 28.8 0.0 0.0 0.0 7.4 0 3 !sd65 3.8 0.0 31.2 0.0 0.0 0.0 7.3 0 3 !sd67 9.7 1.5 77.8 4.3 0.0 0.1 9.0 0 8 !sd68 10.7 1.4 85.3 4.2 0.0 0.1 9.0 0 10 !sd69 10.0 1.5 79.9 4.2 0.0 0.1 9.0 0 9 !sd70 10.4 1.0 83.1 3.2 0.0 0.1 9.1 0 9 !sd71 9.9 1.4 78.8 4.6 0.0 0.1 8.7 0 9 !sd72 10.0 1.1 79.9 3.7 0.0 0.1 8.5 0 8 !sd75 0.0 27.6 0.0 297.3 0.0 0.0 1.1 0 2 !sd210 12.1 0.3 108.9 0.6 0.0 0.1 9.8 0 10 !sd211 12.9 0.4 114.8 0.7 0.0 0.1 10.6 0 11 !sd212 12.0 0.6 107.1 1.3 0.0 0.1 11.1 0 10 !sd213 13.8 0.3 122.2 0.9 0.0 0.2 11.1 0 11 !sd214 12.5 0.5 112.1 1.0 0.0 0.1 10.3 0 10 !sd215 12.1 0.3 109.5 0.8 0.0 0.1 10.5 0 10 !


sd7 root ufs

solid state disks

stripe 8K RR

stripe

cached write log

stripe

CMG-T 2010

Simple Disks

•  Utilization shows capacity usage Measured using iostat %b

•  Response time is svc_t svc_t increases due to waiting in the queues caused by bursty

loads

•  Service time per I/O is Util/IOPS Calculate as(%b/100)/(rps+wps) Decreases due to optimization of queued requests as load

increases


CMG-T 2010

Single Disk Parameters

•  e.g. Seagate 18GB ST318203FC – Obtain from www.seagate.com – RPM = 10000 = 6.0ms = 166/s –  Avg read seek = 5.2ms –  Avg write seek = 6.0ms –  Avg transfer rate = 24.5 MB/s – Random IOPS

•  Approx 166/s for small requests •  Approx 24.5/size for large requests


CMG-T 2010

Mirrored Disks

•  All writes go to both disks

•  Read policy alternatives –  All reads from one side –  Alternate from side to side –  Split by block number to reduce seek – Read both and use first to respond

•  Simple Capacity Assumption –  Assume duplicated interconnects –  Same capacity as unmirrored


CMG-T 2010

Concatenated and Fat Stripe Disks

•  Request size less than interlace

•  Requests go to one disk

•  Single threaded requests –  Same capacity as single disk

•  Multithreaded requests –  Same service time as one disk –  Throughput of N disks if more than N threads are evenly

distributed


CMG-T 2010

Striped Disks

•  Request size more than interlace

•  Requests split over N disks –  Single and multithreaded requests – N = request size / interlace –  Throughput of N disks

•  Service Time Reduction – Reduced size of request reduces service time for large transfers – Need to wait for all disks to complete - slowest dominates


CMG-T 2010

RAID5 for Small Requests

•  Writes must calculate parity – Read parity and old data blocks – Calculate new parity – Write log and data and parity –  Triple service time – One third throughput of one disk

•  Read performs like stripe –  Throughput of N-1, service of one – Degraded mode throughput about one


log

CMG-T 2010

RAID5 for Large Requests

•  Write full stripe and parity

•  Capacity similar to stripe –  Similar read and write performance –  Throughput of N-1 disks –  Service time for size reduced by N-1 –  Less interconnect load than mirror

•  Degraded Mode –  Throughput halved and service similar –  Extra CPU used to regenerate data


log

CMG-T 2010

Cached RAID5

•  Nonvolatile cache – No need for recovery log disk

•  Fast service time for writes –  Interconnect transfer time only

•  Cache optimizes RAID5 – Makes all backend writes full stripe


CMG-T 2010

Cached Stripe

•  Write caching for stripes – Greatly reduced service time –  Very worthwhile for small transfers –  Large transfers should not be cached –  In many cases, 128KB is crossover point from small to large

•  Optimizations – Rewriting same block cancels in cache –  Small sequential writes coalesce


CMG-T 2010

Capacity Model Measurements

•  Derived from iostat outputs!

extended disk statistics disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b

sd9 33.1 8.7 271.4 71.3 0.0 2.3 15.8 0 27

•  Utilization U = %b / 100 = 0.27 •  Throughput X = r/s + w/s = 41.8 •  Size K = Kr/s + Kw/s / X = 8.2K •  Concurrency N = actv = 2.3 •  Service time S = U / X = 6.5ms •  Response time R = svc_t = 15.8ms


CMG-T 2010

Cache Throughput

•  Hard to model clustering and write cancellation improvements

•  Make pessimistic assumption that throughput is unchanged

•  Primary benefit of cache is fast response time

•  Writes can flood cache and saturate back-end disks –  Service times suddenly go from 3ms to 300ms –  Very hard to figure out when this will happen –  Paranoia is a good policy….


CMG-T 2010

Concluding Summary Walk out of here with the most useful content fresh in your mind!


CMG-T 2010

Quick Tips #1 - Disk

•  The system will usually have a disk bottleneck

•  Track how busy is the busiest disk of all

•  Look for unbalanced, busy or slow disks with iostat

•  Options: timestamp, look for busy controllers, ignore idle disks: % iostat -xnzCM -T d 30 Tue Jan 21 09:19:21 2003 extended device statistics r/s w/s Mr/s Mw/s wait actv wsvc_t asvc_t %w %b device 141.0 8.6 0.6 0.0 0.0 1.5 0.0 10.0 0 25 c0 3.3 0.0 0.0 0.0 0.0 0.0 0.0 6.5 0 2 c0t0d0 137.7 8.6 0.6 0.0 0.0 1.5 0.0 10.1 0 74 c0t1d0

Watch out for sd_max_throttle limiting throughput when set too low

Watch out for RAID cache being flooded on writes, causes sudden very large increase in write service time


CMG-T 2010

Quick Tips #2 - Network

•  If you ever see a slow machine that also appears to be idle, you should suspect a network lookup problem. i.e. the system is waiting for some other system to respond.

•  Poor Network Filesystem response times may be hard to see –  Use iostat -xn 30 on a Solaris client –  wsvc_t is the time spent in the client waiting to send a request –  asvc_t is the time spent in the server responding –  %b will show 100% whenever any requests are being processed, it does NOT

mean that the network server is maxed out, as an NFS server is a complex system that can serve many requests at once.

•  Name server delays are also hard to detect –  Overloaded LDAP or NIS servers can cause problems –  DNS configuration errors or server problems often cause 30s delays as the

request times out


CMG-T 2010

Quick Tips #3 - Memory

•  Avoid the common vmstat misconceptions –  The first line is average since boot, so ignore it

•  Linux, Other Unix and earlier Solaris Releases –  Ignore “free” memory –  Use high page scanner “sr” activity as your RAM shortage indicator

•  Solaris 8 and Later Releases –  Use “free” memory to see how much is left for code to use –  Use non-zero page scanner “sr” activity as your RAM shortage indicator

•  Don’t panic when you see page-ins and page-outs in vmstat •  Normal filesystem activity uses paging solaris9% vmstat 30 kthr memory page disk faults cpu r b w swap free re mf pi po fr de sr f0 s0 s1 s6 in sy cs us sy id 0 0 0 2367832 91768 3 31 2 1 1 0 0 0 0 0 0 511 404 350 0 0 99 0 0 0 2332728 75704 3 29 0 0 0 0 0 0 0 0 0 508 537 410 0 0 99


CMG-T 2010

Quick Tips #4 - CPU

•  Look for a long run queue (vmstat procs r) - and add CPUs –  To speedup with a zero run queue you need faster CPUs, not more of them

•  Check for CPU system time dominating user time –  Most systems should have lots more Usr than Sys, as they are running

application code –  But... dedicated NFS servers should be 100% Sys –  And... dedicated web servers have high Sys as well –  So... assume that lots of network service drives Sys time

•  Watch out for processes that hog the CPU –  Big problem on user desktop systems - look for looping web browsers –  Web search engines may get queries that loop –  Use resource management or limit cputime (ulimit -t) in startup scripts to

terminate web queries


CMG-T 2010

Quick Tips #5 - I/O Wait

•  Look for processes blocked waiting for disk I/O (vmstat procs b) –  This is what causes CPU time to be counted as wait not idle –  Nothing else ever causes CPU wait time!

•  CPU wait time is a subset of idle time, consumes no resources –  CPU wait time is a misconceived statistic, and its fallacy is amplified on

multi-threaded systems –  CPU wait time is no longer calculated in Solaris 10; reports as zero –  Bottom line - don’t worry about CPU wait time, it’s a broken metric

•  Look at individual process wait time using microstates –  prstat -m or SE toolkit process monitoring

•  Look at I/O wait time using iostat asvc_t


CMG-T 2010

Quick Tips #6 - iostat

•  For Solaris remember “expenses” iostat -xPncez 30 –  Add -M for Megabytes, and -T d for timestamped logging – Use 30 second interval to avoid spikes in load. – Watch asvc_t which is the response time for Solaris

•  Look for regular disks over 5% busy that have response times of more than 10ms as a problem.

•  If you have cached hardware RAID, look for response times of more than 5ms as a problem.

•  Ignore large response times on idle disks that have filesystems - its not a problem and the cause is the fsflush process


CMG-T 2010

Recipe to fix a slow system

•  Essential Background Information –  What is the business function of the system? –  Who and where are the users? –  Who says there is a problem, and what is slow? –  What changed recently and what is on the way?

•  What is the system configuration? –  CPU/RAM/Disk/Net/OS/Patches, what application software is in use?

•  What are the busy processes on the system doing? –  use top, prstat, pea.se or /usr/ucb/ps uax | head

•  Report CPU and disk utilization levels, iostat -xPncezM -T d 30 –  What is making the disks busy?

•  What is the network name service configuration? –  How much network activity is there? Use netstat -i 30 or nx.se 30

•  Is there enough memory? –  Check free memory and the scan rate with vmstat 30


CMG-T 2010

Further Reading - Books

General Solaris/Unix/Linux Performance Tuning –  System Performance Tuning (2nd Edition) by Gian-Paolo D. Musumeci and Mike

Loukides; O'Reilly & Associates Solaris Performance Tuning Books

–  Solaris Performance and Tools, Richard McDougall, Jim Mauro, Brendan Gregg; Prentice Hall

–  Configuring and Tuning Databases on the Solaris Platform, Allan Packer; Prentice Hall –  Sun Performance and Tuning, by Adrian Cockcroft and Rich Pettit; Prentice Hall

Sun BluePrints™ –  Capacity Planning for Internet Services, Adrian Cockcroft and Bill Walker; Prentice Hall –  Resource Management, Richard McDougall, Adrian Cockcroft et al. Prentice Hall

Linux –  Linux Performance Tuning and Capacity Planning by Jason R. Fink and Matthew D.

Sherer –  Google has a Linux specific search mode http://www.google.com/linux


CMG-T 2010

Questions? (The End)


CMG-T 2010

Backing Material “Test Your Intuition”


CMG-T 2010

Pop Quiz #1

•  SITUATION: A system runs at 100% CPU usage for 1 hour each day completing a single compute-bound task. The SLA requires the task to complete in 4 hours.

•  Q1: How much “headroom” does this system have?

•  Q2: How can this task's resource footprint be managed to never exceed 80% CPU usage?


CMG-T 2010

Pop Quiz #1: Answers •  SITUATION: A system runs at 100% CPU usage for 1 hour each

day completing a single compute-bound task. The SLA requires the task to complete in 4 hours.

•  Q1: How much “headroom” does this system have?

•  A1: 300% (in workload terms) or 75% (in percent-of-system terms) - it can do 4x the work it now does and remain within the SLA.

•  Q2: How can this task's resource footprint be managed to never exceed 80% CPU usage?

•  A2a: Huh? Why would anyone want to do that?

•  A2b: Resource management.


CMG-T 2010

Pop Quiz #2

•  SITUATION: An 8-way 1000-BogoMIPs box runs at 75% CPU busy, with a workload that includes four compute-bound threads plus some OLTP. The new target system is a 4-way 2000-BogoMIPs system.

•  Q1: What is the new system's projected CPU utilization?

•  Q2: How can this system's workload be managed to never exceed 75% CPU utilization?


CMG-T 2010

Pop Quiz #2: Answers •  SITUATION: An 8-way 1000-BogoMIPs box runs at 75% CPU

busy, with a workload that includes four compute-bound threads plus some OLTP. The new target system is a 4-way 2000-BogoMIPs system.

•  Q1: What is the new system's projected CPU utilization? •  A1: 100%. Each of the four compute-bound threads will keep one

CPU 100% busy. •  Q2: How can this system's workload be managed to never exceed

75% CPU utilization? •  A2a: Huh? Why would anyone want to do that? •  A2b: Resource management.


CMG-T 2010

Pop Quiz #3

•  SITUATION: An 8-way 1000-BogoMIPs box runs at 75% CPU busy, with a workload that includes four compute-bound threads plus some OLTP. The new target system is a 4-way 2000-BogoMIPs system. (Same as last quiz, OK?)

•  Q1: How will the compute-bound thread's performance be impacted by the upgrade? (Just roughly speaking – no need for precision here!)


CMG-T 2010

Pop Quiz #3: Answers •  SITUATION: An 8-way 1000-BogoMIPs box runs at 75% CPU

busy, with a workload that includes four compute-bound threads plus some OLTP. The new target system is a 4-way 2000-BogoMIPs system. (Same as last quiz, OK?)

•  Q1: How will the compute-bound thread's performance be impacted by the upgrade? (Just roughly speaking – no need for precision here!)

•  A1: It should run almost 4x faster. Each new CPU is 4x faster than the old ones. (2000/4)/(1000/8) = 4. The OLTP will use some of the CPU cycles, but its service demand pales next to the compute jobs.


CMG-T 2010

Pop Quiz #4

• ESSAY QUESTION: “At what point do these principles become difficult?”


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