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SubjectRe: [PATCH] kvm: handle last_boosted_vcpu = 0 case
On Tue, Jun 19, 2012 at 04:51:04PM -0400, Rik van Riel wrote:
> On Wed, 20 Jun 2012 01:50:50 +0530
> Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote:
>
> >
> > In ple handler code, last_boosted_vcpu (lbv) variable is
> > serving as reference point to start when we enter.
>
> > Also statistical analysis (below) is showing lbv is not very well
> > distributed with current approach.
>
> You are the second person to spot this bug today (yes, today).
>
> Due to time zones, the first person has not had a chance yet to
> test the patch below, which might fix the issue...
>
> Please let me know how it goes.
>
> ====8<====
>
> If last_boosted_vcpu == 0, then we fall through all test cases and
> may end up with all VCPUs pouncing on vcpu 0. With a large enough
> guest, this can result in enormous runqueue lock contention, which
> can prevent vcpu0 from running, leading to a livelock.
>
> Changing < to <= makes sure we properly handle that case.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>

Applied, thanks.



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