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SubjectRe: [PATCH 2/3] coresight: Add section for integration with the perf tools
On 16 April 2018 at 13:48, Randy Dunlap <rdunlap@infradead.org> wrote:
> 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?

Sure thing.

Thanks for taking the time to read the patch and providing comments.

Mathieu

>
>> +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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