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coresight: Add section for integration with the perf tools

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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>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mathieu Poirier 2018-04-17 10:08:06 -06:00 committed by Jonathan Corbet
parent 10c2c55d9f
commit f29816b496
1 changed files with 51 additions and 1 deletions
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Documentation/trace/coresight.txt
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@ -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@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 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@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 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
-------------------------