Highlights of LinuxCon 2010

8/7/2019 Highlights of LinuxCon 2010

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Highlights of LinuxCon 2010

Alison Chaiken

[email protected]

14th September 2010

Power management

Android boot-time

New filesystems

kvm

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Power management: LinuxCons biggestcontroversy

Contending approaches:

Current mainline approach represented by Rafael J. Wysocki

Intel embellishments and optimization presented by Len

BrownAndroid wake_locks and early_suspend, alternate mechanism

from OHA

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Additions to existing runtime powermanagement patch

Linux ACPI has replaced earlier BIOS-based APM.Kernel already has support for underclocking (cpu_freq == "P

states") and hibernation (cpu_idle == "C states")

Next step is to implement per-bus and per-device granularity.

Traditional device-driver approach is addition of newdev_pm_ops methods to API.

Runtime power management framework provides the kernel

interface for the new driver methods.

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dev_pm_ops methodsinclude/linux/pm.h

struct dev_pm_ops {

...

int (*runtime_suspend)(struct device *dev);int (*runtime_resume)(struct device *dev);

int (*runtime_idle)(struct device *dev);

};

include/linux/device.h

struct device_driver { struct struct bus_type {... ...

const struct dev_pm_ops *pm; const struct dev_pm_ops *pm;

... ...

}; };

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For example, seesrc/kernels/2.6.34.6-47.fc13.x86_64 . . .

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Subtleties of runtime power managementframework

Devices run if they please: OS does not, in general, force ashut-down.

System hibernate and wakeup must bring all devices up and

down.

Settings are configured through /sys/devices//power.Event-listener-callback paradigm for wakeup.

A queue holds per-device requests to sleep and wake.

Reference-counting mechanism blocks suspension of devices.

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Powertop and turbostatLen Brown, Intel

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Intels power measurementspowertop screenshot

Linux trails Windows in idle power management, at least for recent

Intel CPUs.

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Android power management architecture

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Fedora 13alison@tomales ;-) ls -l /sys/power

-rw-r--r-- 1 root root 4096 Sep 5 16:00 disk

-rw-r--r-- 1 root root 4096 Sep 5 17:41 image_size

-rw-r--r-- 1 root root 4096 Sep 5 17:41 pm_async

-rw-r--r-- 1 root root 4096 Sep 5 17:41 pm_test

-rw-r--r-- 1 root root 4096 Sep 5 17:41 pm_trace

-rw-r--r-- 1 root root 4096 Sep 5 17:41 resume

-rw-r--r-- 1 root root 4096 Sep 5 16:00 state

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Android 1.6# ls -l /sys/power

-rw-rw---- radio system 4096 2010-09-04 19:14 state

-rw-rw---- radio system 4096 2010-09-04 19:14 wake_lock

-rw-rw---- radio system 4096 2010-09-04 19:14 wake_unlock

-r--r--r-- root root 4096 2010-09-05 15:11 wait_for_fb_sleep

-r--r--r-- root root 4096 2010-09-05 15:11 wait_for_fb_wake

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Granularity in Android PowerManagement

Flag Value CPU Screen Keyboard

PARTIAL_WAKE_LOCK On* Off Off

SCREEN_DIM_WAKE_LOCK On Dim Off

SCREEN_BRIGHT_WAKE_LOCK On Bright Off

FULL_WAKE_LOCK On Bright Bright

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Improving Android boot up timeMajor delay during boot is due to pre-loading of Java classes:

about 1500.

"System And Method For Dynamic Preloading Of Classes . . .(7,426,720)": Oracle vs. Google lawsuit!

Birds attempt to reduce boot-time not exhaustive, but also

not successful so far.

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One Billion Files: Scalability Limits inLinux FS

Ric Wheeler, Red Hat

fsck exhausts system memory at less than a billion files

ext4 rules, but Oracles btrfs (MeeGo) is hot and xfs (SGI)

and zfs (BSD/Solaris) have supporters.Features: xfs, enterprise performance and scalability; zfs,

native support for encryption; btrfs, snapshotting and

reversion.

Observed dramatic implementation-specific effects at largescale:

ext4 is slow where stat() must be run on each file (e.g.

"ls").

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KVM: the Latest from the DevelopmentTeam

Chris Wright, Red Hat

kvm has replaced xen as the VM integrated directly with the

kernel.

qemu emulator is heavily reliant on the kvm device driver.Machine-to-machine paradigm for servers rather than

user-target in embedded.

Support for direct control and communication with hosts

peripherals, esp. PCI, is being added.Guests can run at 80% native speed although implementation

remains buggy!

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Challenges include guest-host coordination of memory (viaNested Page Tables) and scheduling.

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PC-BSD Running in Qemu-KVM onFedora 13

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Invocation of kvm for PCBSDalison@tomales ;-) sudo /bin/rm /tmp/pcbsd.img; qemu-img create \

-f qcow2 /tmp/pcbsd.img 10G

Formatting /tmp/pcbsd.img, fmt=qcow2 size=10737418240 \

encryption=off cluster_size=0

alison@tomales ;-) sudo qemu-kvm -cdrom /opt/PCBSD8.1-x64-DVD.iso -m \

2048 -vga std -hda /tmp/pcbsd.img -writeconfig pcbsd.config

alison@tomales ;-) cat pcbsd.config

# qemu config file[drive]

index = "2"

media = "cdrom"

file = "/opt/PCBSD8.1-x64-DVD.iso"

[drive]

index = "0"media = "disk"

file = "/tmp/pcbsd.img"

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SummaryPower management is the greatest current area of controversy.

Linux lags other OSs in energy conservation.

Android presents both problems and opportunities for Linux.Healthy competition among filesystems leads to rapid

innovation.

Qemu and kvm are both impressive and incredibly useful.

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Without d_type, must stat() and readdir()to list files

/usr/include/dirent.h

#ifdef __USE_BSD /* File types for d_type. */

enum

{ DT_UNKNOWN = 0, # define DT_UNKNOWN DT_UNKNOWN

DT_FIFO = 1, # define DT_FIFO DT_FIFO

DT_CHR = 2, # define DT_CHR DT_CHR

DT_DIR = 4, # define DT_DIR DT_DIR

DT_BLK = 6, # define DT_BLK DT_BLK

DT_REG = 8, # define DT_REG DT_REG

DT_LNK = 10, # define DT_LNK DT_LNKDT_SOCK = 12, # define DT_SOCK DT_SOCK

DT_WHT = 14 # define DT_WHT DT_WHT

};

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No concept of file type in POSIX standard.

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FS Comparative Performance

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Highlights of LinuxCon 2010

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