[erlang-questions] gen_tcp receive extremely high CPU

[Rapsey]

Yeah 30% is really not that much. There is one optimization you can do
however. If you have an after block, this means erlang will be setting up a
new timer for every packet. I would use erlang:send_after and have a
constant timer that only gets executed every X seconds.

When it comes to serving network traffic erlang will surely work very well.
I would recommend you take a look at the cowboy server and build on that
(can be used as a http server or just plain TCP).


Sergej

On Fri, Oct 12, 2012 at 9:55 AM, Gleb Peregud <gleber.p@REDACTED> wrote:

> On Fri, Oct 12, 2012 at 9:48 AM, Anita Wong <anita.wong@REDACTED>
> wrote:
> > Hi All,
> >
> > Sorry that I'm an Erlang newbie and may make stupid question. But please
> > help me to solve the issue.
> >
> > I have written an Erlang server to replace the one I'm using with
> Node.js,
> > which ate all my memory and I'm praying that Erlang could be a way out.
> > The server works properly under unit test and internal testing, but face
> a
> > high CPU usage in stress test.
> >
> > After trimming down, I found that the CPU burst was due to the TCP
> receive
> > from clients.
> >
> > receiveClientPacket(Sock) ->
> >   inet:setopts(Sock, [{active, once}, {buffer, ?CLIENTHEARTBEATSIZE}]),
> >   receive
> >     {tcp, Sock, Data} ->
> >       {ok, Data};
> >     {tcp_closed, Sock} ->
> >       {error, closed}
> >     after ?CLIENTRECCEIVETIMEOUT ->
> >       {error, timeout}
> >   end.
> >
> >
> > I tried making the process sleep for 10 hours at the beginning of the
> > function (to prevent it from calling receive), the CPU didn't burst at
> all.
> > Therefore I conclude that the burst of CPU is due to TCP receive. (Please
> > correct me if I made any mistake)
> >
> > Here are information about my stress test:
> >
> > start the Erlang server with:
> >
> > erl +zdbbl 2097151 -K true +A 128 +P 5000000
> >
> > connect 5000 clients to the Erlang server
> > each connected client sends a 2 byte data to the server every 1 min
> > after all the connections is done, (i.e. only the 2 byte data per min are
> > performing), the CPU burst to ~30%sy (from "top")
> >
> >
> > I'm using an Amazon Linux AMI (large instance, 64-bit) for the Erlang
> > server. Is the burst due to the linux? As I have no idea how the system
> will
> > use up the CPU. Or is it my poor code's problem? (I believe so...)
> >
> > In real situation, our servers don't only receive ping pong, but also
> > messages, which is a lot more loading... This is only the first step...
> >
> > Millions of thanks to anyone who can save me.
> >
> > Anita~*
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Information about large instance (for reference):
> > 7.5 GB memory
> > 4 EC2 Compute Units (2 virtual cores with 2 EC2 Compute Units each)
> > 850 GB instance storage
> > 64-bit platform
> > I/O Performance: High
>
> Hello Anita
>
> Please try rewriting the code to use {active, false} and gen_tcp:recv
> instead and see if it helps. Also high CPU usage might be due to lock
> contention of the VM - try running a VM with lock-counters enabled (
> http://www.erlang.org/doc/apps/tools/lcnt_chapter.html ) to see if
> there's some lock which is contended.
>
> But the most important question - is 30% CPU burst really a problem?
> 30% is usually not a big CPU usage, unless you need some sort of real
> time guarantees. Also Erlang VM uses spin locks and sometimes it uses
> more CPU than similar code in other language, but spin locks are used
> to reduce latency.
>
> Best regards,
> Gleb Peregud
> _______________________________________________
> erlang-questions mailing list
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> http://erlang.org/mailman/listinfo/erlang-questions
>
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