linux-kernel - Re: [PATCH 1/1] x86/cqm: Cqm requirements

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Date:   Wed, 8 Mar 2017 09:58:26 -0800
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Stephane Eranian <eranian@...gle.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        "Shivappa, Vikas" <vikas.shivappa@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>
Subject: Re: [PATCH 1/1] x86/cqm: Cqm requirements

On Wed, Mar 8, 2017 at 12:30 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> Stephane,
>
> On Tue, 7 Mar 2017, Stephane Eranian wrote:
>> On Tue, Mar 7, 2017 at 12:04 PM, Luck, Tony <tony.luck@...el.com> wrote:
>> >> That's all nice and good, but I still have no coherent explanation why
>> >> measuring across allocation domains makes sense.
>> >
>> > Is this in reaction to this one?
>> >
>> >>> 5)      Put multiple threads into a single measurement group
>> >
>> > If we fix it to say "threads from the same CAT group" does it fix things?
>> >
>> Inside a CAT partition, there may be multiple tasks split into different
>> cgroups.  We need the ability to monitor groups of tasks individually
>> within that CAT partition. I think this is what this bullet is about.
>
> I completely understand that. That's fine and I never debated that one, but
> the requirements list is too vague about what you want to measure.
>
>> >>> 5)      Put multiple threads into a single measurement group
>
> That can be:
>
>      A) threads within a CAT group
>
>      B) threads which belong to different CAT groups
>
> A) is fine. B) does not make any sense to me

It's A). As Tony suggested in a previous email, we can rephrase it to:

5) Put a subset of threads from the same CAT group into a single
measurement group.

>
> Same applies for per CPU measurements.

For CPU measurements. We need perf-like CPU filtering to support tools
that perform low overhead monitoring by polling CPU events. These
tools approximate per-cgroup/task events by reconciling CPU events
with logs of what job run when in what CPU.

>
> Thanks,
>
>         tglx