From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@linaro.org>,
James Clark <James.Clark@arm.com>,
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>,
Mark Rutland <mark.rutland@arm.com>, Jiri Olsa <jolsa@redhat.com>,
Namhyung Kim <namhyung@kernel.org>,
coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
Daniel Kiss <daniel.kiss@arm.com>,
Denis Nikitin <denik@google.com>
Subject: Re: [PATCH v2 2/3] perf cs-etm: Remove callback cs_etm_find_snapshot()
Date: Thu, 1 Jul 2021 13:25:14 -0300 [thread overview]
Message-ID: <YN3sas8tWPfWjFqE@kernel.org> (raw)
In-Reply-To: <20210701093537.90759-3-leo.yan@linaro.org>
Em Thu, Jul 01, 2021 at 05:35:36PM +0800, Leo Yan escreveu:
> 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.
>
> This patch removes cs_etm_find_snapshot() 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.
>
> - cs_etm_find_snapshot() adjusts the "head" and "old" pointers and
> assumes the AUX ring buffer is fully filled with the hardware trace
> data, so it always subtracts the difference "mm->len" from "head" to
> get "old". Let's imagine the snapshot is taken in very short
> interval, the tracers only fill a small chunk of the trace data into
> the AUX ring buffer, in this case, it's wrongly to copy the whole the
> AUX ring buffer to perf file.
>
> - As the "head" and "old" pointers are monotonically increased, the
> function __auxtrace_mmap__read() handles these two pointers properly.
> It calculates the reminders for these two pointers, and the size is
> clamped to be never more than "snapshot_size". We can simply reply on
> the function __auxtrace_mmap__read() to calculate the correct result
> for data copying, it's not necessary to add Arm CoreSight specific
> callback.
Thanks, applied.
- Arnaldo
next prev parent reply other threads:[~2021-07-01 16:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 9:35 [PATCH v2 0/3] coresight: Fix for snapshot mode Leo Yan
2021-07-01 9:35 ` [PATCH v2 1/3] coresight: tmc-etr: Use perf_output_handle::head for AUX ring buffer Leo Yan
2021-07-01 9:35 ` [PATCH v2 2/3] perf cs-etm: Remove callback cs_etm_find_snapshot() Leo Yan
2021-07-01 16:25 ` Arnaldo Carvalho de Melo [this message]
2021-07-02 1:10 ` Leo Yan
2021-07-02 18:00 ` Mathieu Poirier
2021-07-01 9:35 ` [PATCH v2 3/3] coresight: Update comments for removing cs_etm_find_snapshot() Leo Yan
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