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

From: Shivappa Vikas
Date: Thu Feb 02 2017 - 12:50:49 EST




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