linux-kernel - Re: [PATCH 09/17] coresight: Clarify comments around the PID of the sink owner

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Message-ID: <CAJ9a7Vgvdjz9peyDzRzAJ3DDGFfjVD0dNXgcJ7b+g-WvCwZ1QQ@mail.gmail.com>
Date: Wed, 1 May 2024 12:07:29 +0100
From: Mike Leach <mike.leach@...aro.org>
To: James Clark <james.clark@....com>
Cc: linux-perf-users@...r.kernel.org, gankulkarni@...amperecomputing.com, 
	scclevenger@...amperecomputing.com, coresight@...ts.linaro.org, 
	suzuki.poulose@....com, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, John Garry <john.g.garry@...cle.com>, 
	Will Deacon <will@...nel.org>, Leo Yan <leo.yan@...ux.dev>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 09/17] coresight: Clarify comments around the PID of the
 sink owner

On Mon, 29 Apr 2024 at 16:24, James Clark <james.clark@....com> wrote:
>
> "Process being monitored" and "pid of the process to monitor" imply that
> this would be the same PID if there were two sessions targeting the same
> process. But this is actually the PID of the process that did the Perf
> event open call, rather than the target of the session. So update the
> comments to make this clearer.
>
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 5 +++--
>  drivers/hwtracing/coresight/coresight-tmc.h     | 5 +++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index e75428fa1592..8962fc27d04f 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -36,7 +36,8 @@ struct etr_buf_hw {
>   * etr_perf_buffer - Perf buffer used for ETR
>   * @drvdata            - The ETR drvdaga this buffer has been allocated for.
>   * @etr_buf            - Actual buffer used by the ETR
> - * @pid                        - The PID this etr_perf_buffer belongs to.
> + * @pid                        - The PID of the session owner that etr_perf_buffer
> + *                       belongs to.
>   * @snaphost           - Perf session mode
>   * @nr_pages           - Number of pages in the ring buffer.
>   * @pages              - Array of Pages in the ring buffer.
> @@ -1662,7 +1663,7 @@ static int tmc_enable_etr_sink_perf(struct coresight_device *csdev, void *data)
>                 goto unlock_out;
>         }
>
> -       /* Get a handle on the pid of the process to monitor */
> +       /* Get a handle on the pid of the session owner */
>         pid = etr_perf->pid;
>
>         /* Do not proceed if this device is associated with another session */
> diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
> index c77763b49de0..2671926be62a 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc.h
> +++ b/drivers/hwtracing/coresight/coresight-tmc.h
> @@ -171,8 +171,9 @@ struct etr_buf {
>   * @csdev:     component vitals needed by the framework.
>   * @miscdev:   specifics to handle "/dev/xyz.tmc" entry.
>   * @spinlock:  only one at a time pls.
> - * @pid:       Process ID of the process being monitored by the session
> - *             that is using this component.
> + * @pid:       Process ID of the process that owns the session that is using
> + *             this component. For example this would be the pid of the Perf
> + *             process.
>   * @buf:       Snapshot of the trace data for ETF/ETB.
>   * @etr_buf:   details of buffer used in TMC-ETR
>   * @len:       size of the available trace for ETF/ETB.
> --
> 2.34.1
>

Reviewed-by: Mike Leach <mike.leach@...aro.org>

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK