Re: [Xen-devel] [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

On 07/10/2013 04:03 PM, Gleb Natapov wrote:
[...] trimmed

> > > Yes. you are right. dynamic ple window was an attempt to solve it.
> > >
> > > Probelm is, reducing the SPIN_THRESHOLD is resulting in excess halt
> > > exits in under-commits and increasing ple_window may be sometimes
> > > counter productive as it affects other busy-wait constructs such as
> > > flush_tlb AFAIK.
> > > So if we could have had a dynamically changing SPIN_THRESHOLD too, that
> > > would be nice.
> > Gleb, Andrew,
> > I tested with the global ple window change (similar to what I posted
> > here https://lkml.org/lkml/2012/11/11/14 ),
> This does not look global. It changes PLE per vcpu.
Okay. Got it. I was thinking it would change the global value. But IIRC
 It is changing global sysfs value and per vcpu ple_window.
Sorry. I missed this part yesterday.

> > But did not see good result. May be it is good to go with per VM
> > ple_window.
> >
> > Gleb,
> > Can you elaborate little more on what you have in mind regarding per
> > VM ple_window. (maintaining part of it as a per vm variable is clear
> > to
> >   me), but is it that we have to load that every time of guest entry?
> Only when it changes, shouldn't be to often no?
Ok. Thinking how to do. read the register and writeback if there need
to be a change during guest entry?



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