From f29816b496f1024ec491203e9f3f6c6c924faf39 Mon Sep 17 00:00:00 2001 From: Mathieu Poirier Date: Tue, 17 Apr 2018 10:08:06 -0600 Subject: [PATCH] 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 Acked-by: Randy Dunlap Signed-off-by: Jonathan Corbet --- Documentation/trace/coresight.txt | 52 ++++++++++++++++++++++++++++++- 1 file changed, 51 insertions(+), 1 deletion(-) 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 -------------------------