Re: [git pull] scheduler fixes

Avi Kivity
2009-01-18T08:30:31Z

Ingo Molnar wrote:
> * Mike Galbraith <efault@gmx.de> wrote:
>
>
>> On Sat, 2009-01-17 at 04:43 -0800, Andrew Morton wrote:
>>
>>> http://bugzilla.kernel.org/show_bug.cgi?id=12465 just popped up - another
>>> scheduler regression. It has been bisected.
>>>
>> Seems pretty clear. I'd suggest reverting it.
>>
>
> We can revert it (and will revert it if no solution is found), but i'd
> also like to understand why it happens, because that kind of regression
> from this change is unexpected - we might be hiding some bug that could
> pop up under less debuggable circumstances, so we need to understand it
> while we have a chance.
>
> Below is the commit in question. Avi, any ideas what makes KVM special
> here? Perhaps its use of "preempt notifiers" is causing a problem somehow?
>

preempt notifiers use should cause additional context switch costs of a
few thousand cycles and possible an IPI (if a vcpu was migrated). So
I'd suspect scheduling latency here.

Is it possible to trace this (the time between a wake up and actual
scheduling of a task)?

--
error compiling committee.c: too many arguments to function