linux-kernel - Re: [PATCH 01/10] perf tools: Uniquify the event name if there's no other matched event

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Date:   Thu, 7 Jun 2018 09:09:10 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        "Liang, Kan" <kan.liang@...ux.intel.com>, agustinv@...eaurora.org,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Milian Wolff <milian.wolff@...b.com>,
        Andi Kleen <andi@...stfloor.org>, frederic@...nel.org
Subject: Re: [PATCH 01/10] perf tools: Uniquify the event name if there's no
 other matched event

On Wed, Jun 6, 2018 at 11:22 PM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Wed, Jun 06, 2018 at 04:19:02PM -0700, Andi Kleen wrote:
> > On Thu, Jun 07, 2018 at 12:15:04AM +0200, Jiri Olsa wrote:
> > > Currently by default we try to match the user specified PMU
> > > name to all PMU units available and use them to aggregate
> > > all matched PMUs event counts into one 'pattern' event.
> > >
> > > While this is useful for uncore events, it screws up names
> > > for other events, where this is not desirable, like:
> > >
> > > Before:
> > >   # perf stat -e cp/cpu-cycles/ kill
> >
> > I assume you mean cpU/cpu-cycles/
> > >
> > >    Performance counter stats for 'kill':
> > >
> > >            1,573,757      cp/cpu-cycles/
> > >
> > > Keeping the pattern matching logic, but making the name unique
> > > in case there's no other match found. That fixes the example
> > > above and hopefully does not screw up anything else.
> > >
And the problem I have with this approach, is that you do not really
know what you are measuring.
You have not way of knowing that the count comes from multiple PMU instances:

perf stat -a -e uncore_cb/clockticks/ kill
0 uncore_cb/clockticks/

I think you need to report that this is aggregated from uncore_cbox_0
and uncore_cbox_1.
Otherwise it is not clear what I am monitoring. And you hope that what
you match in the regex
is related.
In my example should say:
0 uncore_cbox[0-1]/clockticks/

then it is clear what happened.

> > > After:
> > >   # perf stat -e cp/cpu-cycles/ kill
> > >
> > >    Performance counter stats for 'kill':
> > >
> > >            1,573,757      cpu/cpu-cycles/
> >
> >
> > The output is 100% identical?
>
> nope, the U is actualy missing.. that's the thing, the patern
> matching allows you to put 'cp' instead of 'cpu' and the final
> output is screwed.. also the metrics won't match the proper event
>
> jirka