Re: %cpu in system - squid performance in FreeBSD 5.3

From: Sean Chittenden (sean_at_chittenden.org)
Date: 01/04/05

  • Next message: Darcy Buskermolen: "Re: %cpu in system - squid performance in FreeBSD 5.3" 
    Date: Tue, 4 Jan 2005 11:18:28 -0800
To: "Jeff Behl" <jbehl@fastclick.com>

    > PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU CPU
    > COMMAND
    > 474 squid 96 0 68276K 62480K select 0 53:38 16.80% 16.80%
    > squid
    > 311 bind 20 0 10628K 6016K kserel 0 12:28 0.00% 0.00%
    > named
    >
    > It's actually so good that one machine can now handle all traffic
    > (around 180 Mb/s) at < %50 cpu utilization. Seems like something in
    > the
    > network stack is responsible for the high %system cpu util...

    OH!!!! Wow, I should've noticed that earlier. Your hint about someone
    on Linux having the same problem tipped me off to look at the process
    state again. Anyway, you nearly answered your own question, save you
    probably aren't familiar with select(2)'s lack of scalability. Read
    these:

    http://www.kegel.com/c10k.html

    Specifically the four methods mentioned here:

    http://www.kegel.com/c10k.html#nb.select

    Then look at the benchmarks done using libevent(3):

    http://www.monkey.org/~provos/libevent/

    Dime to dollar you're spending all of your time copying file descriptor
    arrays in and out of the kernel because squid uses select(2) instead of
    kqueue(2). Might be an interesting project for someone to take up to
    convert that to kqueue(2). Until then, any local TCP load balancer
    that uses kqueue(2) would also solve your problem (I'm not aware of any
    off the top of my head... pound(8) does, but it is only used for HTTP
    and is not a reverse proxy) and would likely prevent you from having
    your problems. -sc 

    -- 
Sean Chittenden
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  • Next message: Darcy Buskermolen: "Re: %cpu in system - squid performance in FreeBSD 5.3"

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