Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks

From: Avi Kivity
Date: Tue May 08 2012 - 05:10:22 EST

On 05/08/2012 02:15 AM, Jeremy Fitzhardinge wrote:
> On 05/07/2012 06:49 AM, Avi Kivity wrote:
> > On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:
> >> * Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> [2012-05-07 19:08:51]:
> >>
> >>> I 'll get hold of a PLE mc and come up with the numbers soon. but I
> >>> 'll expect the improvement around 1-3% as it was in last version.
> >> Deferring preemption (when vcpu is holding lock) may give us better than 1-3%
> >> results on PLE hardware. Something worth trying IMHO.
> > Is the improvement so low, because PLE is interfering with the patch, or
> > because PLE already does a good job?
> How does PLE help with ticket scheduling on unlock? I thought it would
> just help with the actual spin loops.

PLE yields to up a random vcpu, hoping it is the lock holder. This
patchset wakes up the right vcpu. For small vcpu counts the difference
is a few bad wakeups (and even a bad wakeup sometimes works, since it
can put the spinner to sleep for a bit). I expect that large vcpu
counts would show a greater difference.

error compiling committee.c: too many arguments to function

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