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SubjectRe: [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks
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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