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

[Avi Kivity <avi@xxxxxxxxxx>]

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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