linux-kernel - Re: [PATCH v1 0/3] coresight: Fix for snapshot mode

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Message-ID: <20210612032721.GB36748@leoy-ThinkPad-X240s>
Date:   Sat, 12 Jun 2021 11:27:21 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Denis Nikitin <denik@...gle.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Kiss <daniel.kiss@....com>,
        Coresight ML <coresight@...ts.linaro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 0/3] coresight: Fix for snapshot mode

On Fri, Jun 11, 2021 at 01:31:41AM -0700, Denis Nikitin wrote:
> Hi Suzuki,
> 
> On Thu, Jun 10, 2021 at 9:04 AM Suzuki K Poulose <suzuki.poulose@....com> wrote:
> >
> [...]
> >
> > Are you able to confirm if the patch 3 alone fixes the above issue ?
> > I am not convinced that Patch 1 is necessary.
> >
> 
> Yes. "perf cs-etm: Remove callback cs_etm_find_snapshot()" alone fixes
> the issue.

Based on current testing result, we should give high priority for
patches 2 and 3.

The patch 1 is controversial for how to handle the trace data kept
in multiple AUX buffers; essentially it's up to how we understand the
snapshot definition.  I confirmed Intel-PT and CoreSight have the same
behaviour for capturing trace data from multiple AUX ring buffers when
snapshot occurs.

I'd like to leave patch 1/3 out, and resend it if we get conclusion.
At the meantime, @Denis, if you have observed any profiling result
(or profiling quality) difference caused by patch 1, the feedback would
be very valuable.

Thanks a lot for Denis' testing and insight review from Suzuki!

Leo