On Mon, 15 Nov 2010 18:50:41 +0100 Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
