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

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Date:   Fri, 20 Jan 2017 09:30:00 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
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 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.
 
Thanks,

	tglx