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

[Shivappa Vikas]

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

> > From: Andi Kleen [mailto:andi@xxxxxxxxxxxxxx]
> > "Luck, Tony" <tony.luck@xxxxxxxxx> 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