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

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Date:   Thu, 2 Feb 2017 09:51:18 -0800 (PST)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     "Yu, Fenghua" <fenghua.yu@...el.com>
cc:     Andi Kleen <andi@...stfloor.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        "Shivappa, Vikas" <vikas.shivappa@...el.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Anvin, H Peter" <h.peter.anvin@...el.com>
Subject: RE: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes



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

>> From: Andi Kleen [mailto:andi@...stfloor.org]
>> "Luck, Tony" <tony.luck@...el.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
>