Message-ID: <9e53f5b9-d8a9-46b8-8ff1-7f018e2d9c06@os.amperecomputing.com>
Date: Wed, 11 Dec 2024 10:01:41 -0800
From: Steve Clevenger <scclevenger@...amperecomputing.com>
To: James Clark <james.clark@...aro.org>, coresight@...ts.linaro.org
Cc: yeoreum.yun@....com, Mike Leach <mike.leach@...aro.org>,
 Jonathan Corbet <corbet@....net>, Leo Yan <leo.yan@...ux.dev>,
 Namhyung Kim <namhyung@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: docs: Remove target sink from examples


Hi James,

I thought I'd mention this issue with multicore self-hosted trace. The
perf command line syntax does not allow a sink "type" to be specified
(e.g. @tmc_etf or @tmc_etr). For multicore, it doesn't make sense to
specify a processor mapped sink as would be the case for single core
trace. A sink "type" should be allowed to avoid the auto select default.
In our case, the default is the ETF sink.

Thanks,
Steve C.

On 12/10/2024 6:49 AM, James Clark wrote:
> Previously the sink had to be specified, but now it auto selects one by
> default. Including a sink in the examples causes issues when copy
> pasting the command because it might not work if that sink isn't
> present. Remove the sink from all the basic examples and create a new
> section specifically about overriding the default one.
> 
> Make the text a but more concise now that it's in the advanced section,
> and similarly for removing the old kernel advice.
> 
> Signed-off-by: James Clark <james.clark@...aro.org>
> ---
>  Documentation/trace/coresight/coresight.rst   | 41 ++++++++-----------
>  .../userspace-api/perf_ring_buffer.rst        |  4 +-
>  2 files changed, 18 insertions(+), 27 deletions(-)
> 
> diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
> index d4f93d6a2d63..806699871b80 100644
> --- a/Documentation/trace/coresight/coresight.rst
> +++ b/Documentation/trace/coresight/coresight.rst
> @@ -462,44 +462,35 @@ queried by the perf command line tool:
>  
>  		cs_etm//                                    [Kernel PMU event]
>  
> -	linaro@...aro-nano:~$
> -
>  Regardless of the number of tracers available in a system (usually equal to the
>  amount of processor cores), the "cs_etm" PMU will be listed only once.
>  
>  A Coresight PMU works the same way as any other PMU, i.e the name of the PMU is
> -listed along with configuration options within forward slashes '/'.  Since a
> -Coresight system will typically have more than one sink, the name of the sink to
> -work with needs to be specified as an event option.
> -On newer kernels the available sinks are listed in sysFS under
> +provided along with configuration options within forward slashes '/' (see
> +`Config option formats`_).
> +
> +Advanced Perf framework usage
> +-----------------------------
> +
> +Sink selection
> +~~~~~~~~~~~~~~
> +
> +An appropriate sink will be selected automatically for use with Perf, but since
> +there will typically be more than one sink, the name of the sink to use may be
> +specified as a special config option prefixed with '@'.
> +
> +The available sinks are listed in sysFS under
>  ($SYSFS)/bus/event_source/devices/cs_etm/sinks/::
>  
>  	root@...alhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
>  	tmc_etf0  tmc_etr0  tpiu0
>  
> -On older kernels, this may need to be found from the list of coresight devices,
> -available under ($SYSFS)/bus/coresight/devices/::
> -
> -	root:~# ls /sys/bus/coresight/devices/
> -	 etm0     etm1     etm2         etm3  etm4      etm5      funnel0
> -	 funnel1  funnel2  replicator0  stm0  tmc_etf0  tmc_etr0  tpiu0
>  	root@...aro-nano:~# perf record -e cs_etm/@..._etr0/u --per-thread program
>  
> -As mentioned above in section "Device Naming scheme", the names of the devices could
> -look different from what is used in the example above. One must use the device names
> -as it appears under the sysFS.
> -
> -The syntax within the forward slashes '/' is important.  The '@' character
> -tells the parser that a sink is about to be specified and that this is the sink
> -to use for the trace session.
> -
>  More information on the above and other example on how to use Coresight with
>  the perf tools can be found in the "HOWTO.md" file of the openCSD gitHub
>  repository [#third]_.
>  
> -Advanced perf framework usage
> ------------------------------
> -
>  AutoFDO analysis using the perf tools
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  
> @@ -508,7 +499,7 @@ perf can be used to record and analyze trace of programs.
>  Execution can be recorded using 'perf record' with the cs_etm event,
>  specifying the name of the sink to record to, e.g::
>  
> -    perf record -e cs_etm/@..._etr0/u --per-thread
> +    perf record -e cs_etm//u --per-thread
>  
>  The 'perf report' and 'perf script' commands can be used to analyze execution,
>  synthesizing instruction and branch events from the instruction trace.
> @@ -572,7 +563,7 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
>  	Bubble sorting array of 30000 elements
>  	5910 ms
>  
> -	$ perf record -e cs_etm/@..._etr0/u --per-thread taskset -c 2 ./sort
> +	$ perf record -e cs_etm//u --per-thread taskset -c 2 ./sort
>  	Bubble sorting array of 30000 elements
>  	12543 ms
>  	[ perf record: Woken up 35 times to write data ]
> diff --git a/Documentation/userspace-api/perf_ring_buffer.rst b/Documentation/userspace-api/perf_ring_buffer.rst
> index bde9d8cbc106..dc71544532ce 100644
> --- a/Documentation/userspace-api/perf_ring_buffer.rst
> +++ b/Documentation/userspace-api/perf_ring_buffer.rst
> @@ -627,7 +627,7 @@ regular ring buffer.
>  AUX events and AUX trace data are two different things.  Let's see an
>  example::
>  
> -        perf record -a -e cycles -e cs_etm/@..._etr0/ -- sleep 2
> +        perf record -a -e cycles -e cs_etm// -- sleep 2
>  
>  The above command enables two events: one is the event *cycles* from PMU
>  and another is the AUX event *cs_etm* from Arm CoreSight, both are saved
> @@ -766,7 +766,7 @@ only record AUX trace data at a specific time point which users are
>  interested in.  E.g. below gives an example of how to take snapshots
>  with 1 second interval with Arm CoreSight::
>  
> -  perf record -e cs_etm/@..._etr0/u -S -a program &
> +  perf record -e cs_etm//u -S -a program &
>    PERFPID=$!
>    while true; do
>        kill -USR2 $PERFPID

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