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Re: [Xen-devel] [PATCH v10 11/20] x86/VPMU: Interface for setting PMU mode and flags

>>> On 12.09.14 at 17:54, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 09/12/2014 11:30 AM, Jan Beulich wrote:
>>>>> On 12.09.14 at 17:03, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> My concern is that on a very large system we may be getting lots of
>>> preemptions and thus this will be failing for the sysadmin somewhat
>>> often and without clear reason. (I am basing this assumption on the fact
>>> that I am currently looking at a ~200CPU box with gobs of memory and
>>> some operations that use contuations get preempted very often. Hundreds
>>> of times. I don't remember seeing this on "regular" systems).
>> Yeah, quite likely due to IPI counts growing approximately with the
>> square of the CPU count.
>> We've been considering adding a "minimum amount of progress"
>> mechanism to various places where preemption can (at least under
>> some conditions) be observed on every iteration. Perhaps along
>> with having the 5s timeout you also want a minimum amount of
>> time during which you don't check for preemption (yet)?
> Yes, I can do that. Something like half second?

Urgh - that's way more than a scheduler slice. A couple of
milliseconds at most.


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