Re: Preemptable Ticket Spinlock

[Peter Zijlstra]

On Mon, 2013-04-22 at 22:44 +0200, Peter Zijlstra wrote:
> On Mon, 2013-04-22 at 16:32 -0400, Rik van Riel wrote:
> > 
> > IIRC one of the reasons was that the performance improvement wasn't
> > as obvious.  Rescheduling VCPUs takes a fair amount of time, quite
> > probably more than the typical hold time of a spinlock.
> 
> IIRC it would spin for a while before blocking..
> 
> /me goes re-read some of that thread...
> 
> Ah, its because PLE is curing most of it.. !PLE it had huge gains but
> apparently nobody cares about !PLE hardware anymore :-)

Hmm.. it looked like under light overcommit the paravirt ticket lock
still had some gain (~10%) and of course it brings the fairness thing
which is always good.

I can only imagine the mess unfair + vcpu preemption can bring to guest
tasks.

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