linux-kernel - Re: [PATCH v2 2/3] coresight: Add section for integration with the perf tools

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Message-ID: <a434c2bd-96ab-3f7d-6d78-f69adaac4831@infradead.org>
Date:   Tue, 17 Apr 2018 10:26:45 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, corbet@....net
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ben.Gainey@....com
Subject: Re: [PATCH v2 2/3] coresight: Add section for integration with the
 perf tools

On 04/17/18 09:08, Mathieu Poirier wrote:
> Adding a section that document how to use the Coresight framework and
> drivers from the perf tools.
> 
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>

Acked-by: Randy Dunlap <rdunlap@...radead.org>

Thanks.

> ---
>  Documentation/trace/coresight.txt | 52 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
> index 710c75b6c73f..ab0d0f2d5cec 100644
> --- a/Documentation/trace/coresight.txt
> +++ b/Documentation/trace/coresight.txt
> @@ -187,10 +187,19 @@ that can be performed on them (see "struct coresight_ops").  The
>  specific to that component only.  "Implementation defined" customisations are
>  expected to be accessed and controlled using those entries.
>  
> +
>  How to use the tracer modules
>  -----------------------------
>  
> -Before trace collection can start, a coresight sink needs to be identify.
> +There are two ways to use the Coresight framework: 1) using the perf cmd line
> +tools and 2) interacting directly with the Coresight devices using the sysFS
> +interface.  Preference is given to the former as using the sysFS interface
> +requires a deep understanding of the Coresight HW.  The following sections
> +provide details on using both methods.
> +
> +1) Using the sysFS interface:
> +
> +Before trace collection can start, a coresight sink needs to be identified.
>  There is no limit on the amount of sinks (nor sources) that can be enabled at
>  any given moment.  As a generic operation, all device pertaining to the sink
>  class will have an "active" entry in sysfs:
> @@ -295,6 +304,47 @@ Instruction     13570831        0x8026B584      E28DD00C        false   ADD
>  Instruction     0       0x8026B588      E8BD8000        true    LDM      sp!,{pc}
>  Timestamp                                       Timestamp: 17107041535
>  
> +2) Using perf framework:
> +
> +Coresight tracers are represented using the Perf framework's Performance
> +Monitoring Unit (PMU) abstraction.  As such the perf framework takes charge of
> +controlling when tracing gets enabled based on when the process of interest is
> +scheduled.  When configured in a system, Coresight PMUs will be listed when
> +queried by the perf command line tool:
> +
> +	linaro@...aro-nano:~$ ./perf list pmu
> +
> +		List of pre-defined events (to be used in -e):
> +
> +		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.  Names for sink to choose
> +from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
> +
> +	root@...aro-nano:~# ls /sys/bus/coresight/devices/
> +		20010000.etf   20040000.funnel  20100000.stm  22040000.etm
> +		22140000.etm  230c0000.funnel  23240000.etm 20030000.tpiu
> +		20070000.etr     20120000.replicator  220c0000.funnel
> +		23040000.etm  23140000.etm     23340000.etm
> +
> +	root@...aro-nano:~# perf record -e cs_etm/@...70000.etr/u --per-thread program
> +
> +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 [3].
> +
>  How to use the STM module
>  -------------------------
>  
> 


-- 
~Randy