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-rw-r--r--Documentation/trace/coresight.txt103
1 files changed, 75 insertions, 28 deletions
diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
index 6f0120c3a4f1..1d74ad0202b6 100644
--- a/Documentation/trace/coresight.txt
+++ b/Documentation/trace/coresight.txt
@@ -187,13 +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.
-Last but not least, "struct module *owner" is expected to be set to reflect
-the information carried in "THIS_MODULE".
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:
@@ -298,42 +304,48 @@ Instruction 13570831 0x8026B584 E28DD00C false ADD
Instruction 0 0x8026B588 E8BD8000 true LDM sp!,{pc}
Timestamp Timestamp: 17107041535
-How to use the STM module
--------------------------
+2) Using perf framework:
-Using the System Trace Macrocell module is the same as the tracers - the only
-difference is that clients are driving the trace capture rather
-than the program flow through the code.
+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:
-As with any other CoreSight component, specifics about the STM tracer can be
-found in sysfs with more information on each entry being found in [1]:
+ linaro@linaro-nano:~$ ./perf list pmu
-root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
-enable_source hwevent_select port_enable subsystem uevent
-hwevent_enable mgmt port_select traceid
-root@genericarmv8:~#
+ List of pre-defined events (to be used in -e):
-Like any other source a sink needs to be identified and the STM enabled before
-being used:
+ cs_etm// [Kernel PMU event]
-root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink
-root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source
+ linaro@linaro-nano:~$
-From there user space applications can request and use channels using the devfs
-interface provided for that purpose by the generic STM API:
+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.
-root@genericarmv8:~# ls -l /dev/20100000.stm
-crw------- 1 root root 10, 61 Jan 3 18:11 /dev/20100000.stm
-root@genericarmv8:~#
+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:
-Details on how to use the generic STM API can be found here [2].
+ 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
-[1]. Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
-[2]. Documentation/trace/stm.txt
+ 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.
-Using perf tools
-----------------
+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].
+
+2.1) AutoFDO analysis using the perf tools:
perf can be used to record and analyze trace of programs.
@@ -381,3 +393,38 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
$ taskset -c 2 ./sort_autofdo
Bubble sorting array of 30000 elements
5806 ms
+
+
+How to use the STM module
+-------------------------
+
+Using the System Trace Macrocell module is the same as the tracers - the only
+difference is that clients are driving the trace capture rather
+than the program flow through the code.
+
+As with any other CoreSight component, specifics about the STM tracer can be
+found in sysfs with more information on each entry being found in [1]:
+
+root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
+enable_source hwevent_select port_enable subsystem uevent
+hwevent_enable mgmt port_select traceid
+root@genericarmv8:~#
+
+Like any other source a sink needs to be identified and the STM enabled before
+being used:
+
+root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink
+root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source
+
+From there user space applications can request and use channels using the devfs
+interface provided for that purpose by the generic STM API:
+
+root@genericarmv8:~# ls -l /dev/20100000.stm
+crw------- 1 root root 10, 61 Jan 3 18:11 /dev/20100000.stm
+root@genericarmv8:~#
+
+Details on how to use the generic STM API can be found here [2].
+
+[1]. Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
+[2]. Documentation/trace/stm.txt
+[3]. https://github.com/Linaro/perf-opencsd