linux-kernel - Re: [PATCH v1 1/3] coresight: etm-perf: Correct buffer syncing for snapshot

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Message-ID: <20210609013909.GE4640@leoy-ThinkPad-X240s>
Date:   Wed, 9 Jun 2021 09:39:09 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        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>,
        Denis Nikitin <denik@...gle.com>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 1/3] coresight: etm-perf: Correct buffer syncing for
 snapshot

On Wed, Jun 09, 2021 at 09:35:55AM +0800, Leo Yan wrote:

[...]

> > The problem with this approach is that if the AUX buffer is 4MB and the CS
> > buffer is 1MB then we only record 1MB, but because of N:1 topologies we may not
> > be able to do better.  I haven't looked at the code yet, something I will do
> > tomorrow.
> 
> Yes, the fixing in this patch copies the trace data is limited by the
> CoreSight bounce buffer length.  So if CoreSight buffer length is
> 1MiB, then we have no chance to allocate 4MiB for AUX buffer.

Sorry for typo, just correct:

if CoreSight buffer length is 1MiB, then we have no chance to *copy*
4MiB trace data for AUX buffer.