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SubjectRE: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes


On Wed, 1 Feb 2017, Yu, Fenghua wrote:

>> From: Andi Kleen [mailto:andi@firstfloor.org]
>> "Luck, Tony" <tony.luck@intel.com> writes:
>>> 9) Measure per logical CPU (pick active RMID in same precedence for
>> task/cpu as CAT picks CLOSID)
>>> 10) Put multiple CPUs into a group
>>
>> I'm not sure this is a real requirement. It's just an optimization, right? If you
>> can assign policies to threads, you can implicitly set it per CPU through affinity
>> (or the other way around).
>> The only benefit would be possibly less context switch overhead, but if all
>> the thread (including idle) assigned to a CPU have the same policy it would
>> have the same results.
>>
>> I suspect dropping this would likely simplify the interface significantly.
>
> Assigning a pid P to a CPU and monitoring the P don't count all events happening on the CPU.
> Other processes/threads (e.g. kernel threads) than the assigned P can run on the CPU.
> Monitoring P assigned to the CPU is not equal to monitoring the CPU in a lot cases.

This matches the use case where a bunch of real time tasks which have no CLOS
id(kernel threads or others in root group) would want to run exclusively on a
cpu and are configured so. If any other tasks run there from other class of
service we dont want to pullute the cache - hence choose their own CLOSId.

Now in order to measure this RMIds need to match the same policy as CAT.

Thanks,
Vikas

>
> Thanks.
>
> -Fenghua
>

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