path: root/Documentation/trace/coresight.txt
diff options
authorMathieu Poirier <mathieu.poirier@linaro.org>2018-04-17 10:08:06 -0600
committerJonathan Corbet <corbet@lwn.net>2018-04-27 17:00:04 -0600
commitf29816b496f1024ec491203e9f3f6c6c924faf39 (patch)
treeb8aebf2e425736edf277c5ba4d08c4d9e958e5a9 /Documentation/trace/coresight.txt
parent10c2c55d9fbd9ef9150914f58660bda64e64c98a (diff)
coresight: Add section for integration with the perf tools
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>
Diffstat (limited to 'Documentation/trace/coresight.txt')
1 files changed, 51 insertions, 1 deletions
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@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