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Commit f29816b4 authored by Mathieu Poirier's avatar Mathieu Poirier Committed by Jonathan Corbet
Browse files

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: default avatarMathieu Poirier <mathieu.poirier@linaro.org>
Acked-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 10c2c55d

Documentation/trace/coresight.txt

+51 −1
Original line number Diff line number Diff line
@@ -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

-------------------------