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SubjectRe: [PATCH 2/3] coresight: Add section for integration with the perf tools
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On 04/16/2018 12:35 PM, 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@linaro.org>
> ---
> Documentation/trace/coresight.txt | 50 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 50 insertions(+)
>
> diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
> index 710c75b6c73f..8caae8050a60 100644
> --- a/Documentation/trace/coresight.txt
> +++ b/Documentation/trace/coresight.txt
> @@ -187,9 +187,18 @@ 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
> -----------------------------
>
> +There is two ways to use the Coresight framework: 1) using the perf cmd line

There are two ways

> +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 identify.

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
> @@ -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@linaro-nano:~$ ./perf list pmu
> +
> + List of pre-defined events (to be used in -e):
> +
> + cs_etm// [Kernel PMU event]
> +
> + linaro@linaro-nano:~$
> +
> +Regardless of the number of tracers available in a system (usually equal to the
> +amount of processor core), the "cs_etm" PMU will be listed only once.

? cores),

> +
> +A Coresight PMU works the same way as any other PMUs, i.e the name of the PMU is

any other PMU, i.e.

> +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@linaro-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@linaro-nano:~# perf record -e cs_etm/@20070000.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 IP

Can we get away from using "IP" and call it a device or (hardware) module or
something more descriptive?

> +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].


--
~Randy

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