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

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Date:   Tue, 7 Mar 2017 21:22:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>
cc:     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>,
        "davidcc@...gle.com" <davidcc@...gle.com>,
        "eranian@...gle.com" <eranian@...gle.com>
Subject: RE: [PATCH 1/1] x86/cqm: Cqm requirements

On Tue, 7 Mar 2017, Luck, Tony 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?
> 
> We'd like to have measurement groups use a single RMID ... if we
> allowed tasks from different CAT groups in the same measurement
> group we wouldn't be able to split the numbers back to report the
> right overall total for each of the CAT groups.

Right. And the same applies to CPU measurements. If we have threads from 3
CAT groups running on a CPU then the aggregate value (except for bandwidth
which can be computed by software) is useless.

Thanks,

	tglx