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

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Message-ID: <3fa5f992-b758-4928-9bf9-0c6e82db1f65@arm.com>
Date: Tue, 7 May 2024 09:55:30 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: James Clark <james.clark@....com>, linux-perf-users@...r.kernel.org,
 gankulkarni@...amperecomputing.com, scclevenger@...amperecomputing.com,
 coresight@...ts.linaro.org, suzuki.poulose@....com, mike.leach@...aro.org
Cc: 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 4/29/24 20:51, James Clark 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>

This indeed removes the ambiguity that the PID belongs to the perf session
owner rather than the monitored or target process.

Reviewed-by: Anshuman Khandual <anshuman.khandual@....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.