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Date:   Thu, 23 Sep 2021 22:40:48 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     German Gomez <german.gomez@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org
Subject: Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback

On Thu, Sep 23, 2021 at 09:50:16PM +0800, Leo Yan wrote:

[...]

> > @@ -336,6 +480,7 @@ struct auxtrace_record *arm_spe_recording_init(int *err,
> >  	sper->itr.pmu = arm_spe_pmu;
> >  	sper->itr.snapshot_start = arm_spe_snapshot_start;
> >  	sper->itr.snapshot_finish = arm_spe_snapshot_finish;
> > +	sper->itr.find_snapshot = arm_spe_find_snapshot;
> 
> If I understand correctly, this patch copies the code from cs-etm for
> snapshot handling.  About 2 months ago, we removed the Arm cs-etm's
> specific snapshot callback function and directly use perf's function
> __auxtrace_mmap__read() to handle 'head' and 'tail' pointers.  Please
> see the commit for details:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2f01c200d4405c4562e45e8bb4de44a5ce37b217
> 
> Before I review more details for snapshot enabling in patches 03 and
> 04, could you confirm if Arm SPE can use the same way with cs-etm for
> snapshot handling?  From my understanding, this is a better way to
> handle AUX buffer's 'head' and 'tail'.

In other words, if we can only apply patch 03 and can pass the testing
in patch 05, then it would be a very neat implementation.

I will try to verify these patches and will get back result.

Thanks,
Leo

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