lkml.org 
[lkml]   [2016]   [Jan]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Subject[PATCH 0/2] sched,time: reduce nohz_full syscall overhead 40%
    Date
    unning with nohz_full introduces a fair amount of overhead.
    Specifically, various things that are usually done from the
    timer interrupt are now done at syscall, irq, and guest
    entry and exit times.

    However, some of the code that is called every single time
    has only ever worked at jiffy resolution. The code in
    __acct_update_integrals was also doing some unnecessary
    calculations.

    Getting rid of the unnecessary calculations, without
    changing any of the functionality in __acct_update_integrals
    gets us about an 11% win.

    Not calling the time statistics updating code more than
    once per jiffy, like is done on housekeeping CPUs and on
    all the CPUs of a non-nohz_full system, shaves off a
    further 30%.

    I tested this series with a microbenchmark calling
    an invalid syscall number ten million times in a row,
    on a nohz_full cpu.

    Run times for the microbenchmark:

    4.4 3.8 seconds
    4.5-rc1 3.7 seconds
    4.5-rc1 + first patch 3.3 seconds
    4.5-rc1 + first 3 patches 3.1 seconds
    4.5-rc1 + all patches 2.3 seconds

    \
     
     \ /
      Last update: 2016-01-30 05:21    [W:2.329 / U:0.992 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site