linux-kernel - Re: [PATCH v5 6/7] drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension

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Date:   Mon, 2 Oct 2017 13:49:30 -0300
From:   Arnaldo Carvalho de Melo <acme@...hat.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Kim Phillips <kim.phillips@....com>,
        linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        mark.rutland@....com, tglx@...utronix.de, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, robh@...nel.org,
        suzuki.poulose@....com, pawel.moll@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 6/7] drivers/perf: Add support for ARMv8.2 Statistical
 Profiling Extension

Em Mon, Oct 02, 2017 at 03:14:05PM +0100, Will Deacon escreveu:
> On Fri, Sep 29, 2017 at 05:19:40PM -0500, Kim Phillips wrote:
> > On Thu, 28 Sep 2017 15:09:50 +0100
> > Will Deacon <will.deacon@....com> wrote:
> > > +	if (arm_spe_event_to_pmsevfr(event) & SYS_PMSEVFR_EL1_RES0)
> > > +		return -EOPNOTSUPP;
> > > +	if (attr->exclude_idle)
> > > +		return -EOPNOTSUPP;

> > "PMU Hardware doesn't support sampling/overflow-interrupts." will be
> > printed if the user didn't specify a sample period.  Otherwise, a
> > string with "/bin/dmesg may provide additional information." will be
> > printed.

> > I was hoping for a response from acme by now for this:

> > https://www.spinics.net/lists/linux-perf-users/msg04066.html

> > Alas, nothing.  Looking at the #ifdef x86 in evsel.c, I'm guessing
> > it'll be ok, although I'm still not sure how PMU-specific we can get in
> > evsel.c, nor whether it's ok to communicate lists of h/w supported
> > sample periods through /sys/bus/event_source/devices/...
> > 
> > acme?  OK to refactor evsel messaging for Arm, including parsing for
> > which PMUs are being used, so customize the message?
> 
> Arnaldo's probably got enough on his plate maintaining perf tool, so my
> advice would be to post a patch as an RFC and use that as a concrete basis
> for discussion. It often works out better starting with code, even if none
> of it ends up getting merged (and you can include bits of your email above
> in the cover letter).

I'm all for more informative messages, and if you guys agree on how to
provide the info in a way that combined with logic in evsel.c, I'd say
do what Will suggested, post a patch series and include usage examples,
before and after.

- Arnaldo