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

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Date:   Mon, 6 Feb 2017 23:27:29 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        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>,
        "Yu, Fenghua" <fenghua.yu@...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

> cgroup mode gives a per-CPU breakdown of event and running time, the
> tool aggregates it into running time vs event count. Both per-cpu
> breakdown and the aggregate are useful.
>
> Piggy-backing on perf's cgroup mode would give us all the above for free.

Do you have some sample output from a perf run on a cgroup measuring a
"normal" event showing what you get?

I think that requires that we still go through perf ->start() and ->stop() functions
to know how much time we spent running.  I thought we were looking at bundling
the RMID updates into the same spot in sched() where we switch the CLOSID.
More or less at the "start" point, but there is no "stop".  If we are switching between
runnable processes, it amounts to pretty much the same thing ... except we bill
to someone all the time instead of having a gap in the context switch where we
stopped billing to the old task and haven't started billing to the new one yet.

But if we idle ... then we don't "stop".  Shouldn't matter much from a measurement
perspective because idle won't use cache or consume bandwidth. But we'd count
that time as "on cpu" for the last process to run.

-Tony