lkml.org 
[lkml]   [2010]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC][PATCH v2 4/7] taskstats: Add per task steal time accounting
    On Mon, 15 Nov 2010 18:50:41 +0100
    Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > On Mon, 2010-11-15 at 18:42 +0100, Martin Schwidefsky wrote:
    > > The steal time of a task tells us how much more progress a task could have
    > > done if the hypervisor would not steal cpu. Now you could argue that the
    > > steal time for a cpu is good enough for that purpose but steal time is not
    > > necessarily uniform over all tasks. And we already do calculate this number,
    > > we just do not store it right now.
    >
    > If you make the scheduler take steal time into account like Jeremy
    > proposed then you schedule on serviced time and the steal time gain is
    > proportional to the existing service distribution.
    >
    > Still, then you know, then what are you going to do about it? Are you
    > going to avoid the hypervisor from scheduling when that one task is
    > running?
    >
    > What good is knowing something you cannot do anything about.

    Steal time per task is at least good for performance problem analysis.
    Sometimes knowing what is not the cause of a performance problem can help you
    tremendously. If a task is slow and has no steal time, well then the hypervisor
    is likely not the culprit. On the other hand if you do see lots of steal time
    for a task while the rest of the system doesn't cause any steal time can tell
    you something as well. That task might hit a specific function which causes
    hypervisor overhead. The usefulness depends on the situation, it is another
    data point which may or may not help you.

    --
    blue skies,
    Martin.

    "Reality continues to ruin my life." - Calvin.



    \
     
     \ /
      Last update: 2010-11-15 19:01    [W:0.021 / U:59.828 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site