Re: [git pull] scheduler fixes

[Avi Kivity]

Ingo Molnar wrote:
> * Mike Galbraith <efault@xxxxxx> 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

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