lkml.org 
[lkml]   [2007]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: CFS review
    Hi,

    On Wed, 1 Aug 2007, Ingo Molnar wrote:

    > > [...] e.g. in this example there are three tasks that run only for
    > > about 1ms every 3ms, but they get far more time than should have
    > > gotten fairly:
    > >
    > > 4544 roman 20 0 1796 520 432 S 32.1 0.4 0:21.08 lt
    > > 4545 roman 20 0 1796 344 256 R 32.1 0.3 0:21.07 lt
    > > 4546 roman 20 0 1796 344 256 R 31.7 0.3 0:21.07 lt
    > > 4547 roman 20 0 1532 272 216 R 3.3 0.2 0:01.94 l
    >
    > Mike and me have managed to reproduce similarly looking 'top' output,
    > but it takes some effort: we had to deliberately run a non-TSC
    > sched_clock(), CONFIG_HZ=100, !CONFIG_NO_HZ and !CONFIG_HIGH_RES_TIMERS.

    I used my old laptop for these tests, where tsc is indeed disabled due to
    instability. Otherwise the kernel was configured with CONFIG_HZ=1000.

    > in that case 'top' accounting symptoms similar to the above are not due
    > to the scheduler starvation you suspected, but due the effect of a
    > low-resolution scheduler clock and a tightly coupled timer/scheduler
    > tick to it.

    Well, it magnifies the rounding problems in CFS.
    I mainly wanted to test a little the behaviour of CFS and I thought a saw
    patch which enabled the use of TSC in these cases, so I didn't check
    sched_clock().

    Anyway, I want to point out that this wasn't the main focus of what I
    wrote.

    bye, Roman
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-08-01 14:23    [W:0.020 / U:3.036 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site