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

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Date:   Fri, 20 Jan 2017 12:27:34 -0800
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Shivappa Vikas <vikas.shivappa@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, hpa@...or.com,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, andi.kleen@...el.com,
        "H. Peter Anvin" <h.peter.anvin@...el.com>
Subject: Re: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes

On Fri, Jan 20, 2017 at 12:30 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 19 Jan 2017, David Carrillo-Cisneros wrote:
>> On Thu, Jan 19, 2017 at 9:41 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > Above you are talking about the same CLOSID and different RMIDS and not
>> > about changing both.
>>
>> The scenario I talked about implies changing CLOSID without affecting
>> monitoring.
>> It happens when the allocation needs for a thread/cgroup/CPU change
>> dynamically. Forcing to change the RMID together with the CLOSID would
>> give wrong monitoring values unless the old RMID is kept around until
>> becomes free, which is ugly and would waste a RMID.
>
> When the allocation needs for a resource control group change, then we
> simply update the allocation constraints of that group without chaning the
> CLOSID. So everything just stays the same.
>
> If you move entities to a different group then of course the CLOSID
> changes and then it's a different story how to deal with monitoring.
>
>> > To gather any useful information for both CPU1 and T1 you need TWO
>> > RMIDs. Everything else is voodoo and crystal ball analysis and we are not
>> > going to support that.
>> >
>>
>> Correct. Yet, having two RMIDs to monitor the same task/cgroup/CPU
>> just because the CLOSID changed is wasteful.
>
> Again, the CLOSID only changes if you move entities to a different resource
> control group and in that case the RMID change is the least of your worries.
>
>> Correct. But there may not be a fixed CLOSID association if loads
>> exhibit dynamic behavior and/or system load changes dynamically.
>
> So, you really want to move entities around between resource control groups
> dynamically? I'm not seing why you would want to do that, but I'm all ear
> to get educated on that.

No, I don't want to move entities across resource control groups. I
was confused by the idea of CLOSIDs being married to control groups,
but now is clear even to me that that was never the intention.

Thanks,
David

>
> Thanks,
>
>         tglx