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Subject: Re: [PATCH v1 3/3] perf cs-etm: Remove callback
 cs_etm_find_snapshot()
To:     Leo Yan <leo.yan@linaro.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Daniel Kiss <daniel.kiss@arm.com>,
        Denis Nikitin <denik@google.com>, coresight@lists.linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org
References: <20210528161552.654907-1-leo.yan@linaro.org>
 <20210528161552.654907-4-leo.yan@linaro.org>
From:   James Clark <james.clark@arm.com>
Message-ID: <4aa2cfcc-0dc2-4884-2ae4-7e977d3c60ad@arm.com>
Date:   Thu, 24 Jun 2021 17:46:32 +0100
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On 28/05/2021 17:15, Leo Yan wrote:
> The callback cs_etm_find_snapshot() is invoked for snapshot mode, its
> main purpose is to find the correct AUX trace data and returns "head"
> and "old" (we can call "old" as "old head") to the caller, the caller
> __auxtrace_mmap__read() uses these two pointers to decide the AUX trace
> data size.
> > cs_etm_find_snapshot() should be removed with below reasons:
> 
> - The first thing in cs_etm_find_snapshot() is to check if the head has
>   wrapped around, if it is not, directly bails out.  The checking is
>   pointless, this is because the "head" and "old" pointers both are
>   monotonical increasing so they never wrap around.
> 
For patch 3:

Reviewed-by: James Clark <james.clark@arm.com>
Tested-by: James Clark <james.clark@arm.com>

I think it's a good simplification and it also fixes the duplicate buffers
issue. And I agree with the reasoning about the pointer increasing monotonically.