0.5 mln packets per second with Erlang

Nov 22, 2014

Maxim Kharchenko

CTO/Cloudozer LLP

The road map

• Erlang on Xen intro

• LINCX project overview

• Speed-related notes

– Arguments are registers

– ETS tables are (mostly) ok

– Do not overuse records

– GC is key to speed

– gen_server vs. barebone process

– NIFS: more pain than gain

– Fast counters

– Static compiler?

• Q&A

Erlang on Xen a.k.a. LING

• A new Erlang platform that runs without OS

• Conceived in 2009

• Highly-compatible with Erlang/OTP

• Built from scratch, not a “port”

• Optimized for low startup latency

• Open sourced in 2014 (github.com/cloudozer/ling)

• Local and remote builds

Go to erlangonxen.org

Zerg demo: zerg.erlangonxen.org

The road map

• Erlang on Xen intro

• LINCX project overview

• Speed-related notes

– Arguments are registers

– ETS tables are (mostly) ok

– Do not overuse records

– GC is key to speed

– gen_server vs. barebone process

– NIFS: more pain than gain

– Fast counters

– Static compiler?

• Q&A

LINCX: project overview

• Started in December, 2013

• Initial scope = porting LINC-Switch to LING

• High degree of compatibility demonstrated for LING

• Extended scope = fix LINC-Switch fast path

• Beta version of LINCX open sourced on March 3, 2014

• LINCX runs 100x faster than the old code

LINCX repository:github.com/FlowForwarding/lincx

Raw network interfaces in Erlang• LING adds raw network interfaces:

Port = net_vif:open(“eth1”, []),port_command(Port, <<1,2,3>>),receive{Port,{data,Frame}} >‐...

• Raw interface receives whole Ethernet frames

• LINCX uses standard gen_tcp for the control connection and net_vif -

for data ports

• Raw interfaces support mailbox_limit option - packets get dropped if

the mailbox of the receiving process overflows:

Port = net_vif:open(“eth1”, [{mailbox_limit,16384}]),...

Testbed configuration

* Test traffic goes between vm1 and vm2

* LINCX runs as a separate Xen domain

* Virtual interfaces are bridged in Dom0

IXIA confirms 460kpps peak rate

• 1GbE hw NICs/128 byte packets

• IXIA packet generator/analyzer

Processing delay and low-level stats

• LING can measure a processing delay for a packet:

1> ling:experimental(processing_delay, []).Processing delay statistics:Packets: 2000 Delay: 1.342us + 0.143 (95%)‐

• LING can collect low-level stats for a network interface:

1> ling:experimental(llstat, 1). %% stop/displayDuration: 4868.6msRX: interrupts: 69170 (0 kicks 0.0%) (freq 14207.4/s period 70.4us)RX: reqs per int: 0/0.0/0RX: tx buf freed per int: 0/8.5/234TX: outputs: 1479707 (112263 kicks 7.6) (freq 303928.8/s period 3.3us)TX: tx buf freed per int: 0/0.6/113TX: rates: 303.9kpps 3622.66Mbps avg pkt size 1489.9BTX: drops: 12392 (freq 2545.3/s period 392.9us)TX: drop rates: 2.5kpps 30.26Mbps avg pkt size 1486.0B

The road map

• Erlang on Xen intro

• LINCX project overview

• Speed-related notes

– Arguments are registers

– ETS tables are (mostly) ok

– Do not overuse records

– GC is key to speed

– gen_server vs. barebone process

– NIFS: more pain than gain

– Fast counters

– Static compiler?

• Q&A

Arguments are registers

animal(batman = Cat, Dog, Horse, Pig, Cow, State) >‐ feed(Cat, Dog, Horse, Pig, Cow, State);animal(Cat, deli = Dog, Horse, Pig, Cow, State) >‐ pet(Cat, Dog, Horse, Pig, Cow, State);...

%% SLOWanimal(batman = Cat, Dog, Horse, Pig, Cow, State) >‐ feed(Goat, Cat, Dog, Horse, Pig, Cow, State);...

• Many arguments do not make a function any slower

• But do not reshuffle arguments:

ETS tables are (mostly) ok

• A small ETS table lookup = 10x function activations

• Do not use ets:tab2list() inside tight loops

• Treat ETS as a database; not a pool of global variables

• 1-2 ETS lookups on the fast path are ok

• Beware that ets:lookup(), etc create a copy of the data on the heap of

the caller, similarly to message passing

Do not overuse records

• selelement() creates a copy of the tuple

• State#state{foo=Foo1,bar=Bar1,baz=Baz1} creates 3(?)

copies of the tuple

• Use tuples explicitly in performance-critical sections to control

the heap footprint of the code:

%% from 9p.erlmixer({rauth,_,_}, {tauth,_,Afid,_,_}, _) > {write_auth,AFid};‐mixer({rauth,_,_}, {tauth,_,Afid,_,_,_}, _) > {write_auth,AFid};‐mixer({rwrite,_,_}, _, initial) > start_attaching;‐mixer({rerror,_,_}, _, initial) > auth_failed;‐mixer({rlerror,_,_}, _, initial) > auth_failed;‐mixer({rattach,_,Qid}, {tattach,_,Fid,_,_,Aname,_}, initial) >‐ {attach_more,Fid,AName,qid_type(Qid)};mixer({rclunk,_}, {tclunk,_,Fid}, initial) > {forget,Fid};‐

Garbage collection is key to speed

• Heap is a list of chunks

• 'new heap' is close to its head, 'old heap' - to its tail

• A GC run takes 10 s on averageμ

• GC may run 1000s times per second

proc_tHTOP

...

How to tackle GC-related issues

• (Priority 1) Call erlang:garbage_collect() at strategic points

• (Priority 2) For the fastest code avoid GC completely – restart the fast

process regularly:

spawn(F, [{suppress_gc,true}]), %% LING only‐

• (Priority 3) Use fullsweep_after option

gen_server vs barebone process

• Message passing using gen_server:call() is 2x slower than Pid ! Msg

• For speedy code prefer barebone processes to gen_servers

• Design Principles are about high availability, not high performance

NIFs: more pain than gain

• A new principle of Erlang development: do not use NIFs

• For a small performance boost, NIFs undermine key properties of

Erlang: reliability and soft-realtime guarantees

• Most of the time Erlang code can be made as fast as C

• Most of performance problems of Erlang are traceable to NIFs, or

external C libraries, which are similar

• Erlang on Xen does not have NIFs and we do not plan to add them

Fast counters• 32-bit or 64-bit unsigned integer counters with overflow - trivial in C,

not easy in Erlang

• FIXNUMs are signed 29-bit integers, BIGNUMs consume heap and are

10-100x slower

• Use two variables for a counter?

foo(C1, 16#ffffff, ...) -> foo(C1+1, 0, ...);foo(C1, C2, ...) > foo(C1,‐ C2+1, ...);...

• LING has a new experimental feature – fast counters:

erlang:new_counter(Bits) > Ref‐erlang:increment_counter(Ref, Incr)erlang:read_counter(Ref)erlang:release_counter(Ref)

Future: static compiler for Erlang

• Scalars and algebraic types

• Structural types only – no nominal types

• Target compiler efficiency not static type checking

• A middle ground between:

• “Type is a first class citizen” (Haskell)

• “A single type is good enough” (Python, Erlang)

Future: static compiler for Erlang - 2

• Challenges:

• Pattern matching compilation

• Type inference for recursive types

y = {(unit | y), x, (unit | y)}

• Work started in 2013

• Currently the compiler is at the proof-of-concept stage

y = nil | {x, y}

Questions

???

e-mail: maxim.kharchenko@gmail.com