Documentation: coresight: Update the generic device names
Update the documentation to reflect the new naming scheme with latest changes. Reported-by: Leo Yan <leo.yan@linaro.org> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Suzuki K Poulose
Jonathan Corbet
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@ -188,6 +188,49 @@ specific to that component only. "Implementation defined" customisations are
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expected to be accessed and controlled using those entries.
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Device Naming scheme
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------------------------
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The devices that appear on the "coresight" bus were named the same as their
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parent devices, i.e, the real devices that appears on AMBA bus or the platform bus.
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Thus the names were based on the Linux Open Firmware layer naming convention,
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which follows the base physical address of the device followed by the device
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type. e.g:
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root:~# ls /sys/bus/coresight/devices/
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20010000.etf 20040000.funnel 20100000.stm 22040000.etm
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22140000.etm 230c0000.funnel 23240000.etm 20030000.tpiu
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20070000.etr 20120000.replicator 220c0000.funnel
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23040000.etm 23140000.etm 23340000.etm
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However, with the introduction of ACPI support, the names of the real
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devices are a bit cryptic and non-obvious. Thus, a new naming scheme was
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introduced to use more generic names based on the type of the device. The
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following rules apply:
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1) Devices that are bound to CPUs, are named based on the CPU logical
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number.
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e.g, ETM bound to CPU0 is named "etm0"
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2) All other devices follow a pattern, "<device_type_prefix>N", where :
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<device_type_prefix> - A prefix specific to the type of the device
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N - a sequential number assigned based on the order
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of probing.
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e.g, tmc_etf0, tmc_etr0, funnel0, funnel1
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Thus, with the new scheme the devices could appear as :
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root:~# ls /sys/bus/coresight/devices/
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etm0 etm1 etm2 etm3 etm4 etm5 funnel0
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funnel1 funnel2 replicator0 stm0 tmc_etf0 tmc_etr0 tpiu0
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Some of the examples below might refer to old naming scheme and some
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to the newer scheme, to give a confirmation that what you see on your
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system is not unexpected. One must use the "names" as they appear on
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the system under specified locations.
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How to use the tracer modules
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-----------------------------
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@ -326,16 +369,25 @@ amount of processor cores), the "cs_etm" PMU will be listed only once.
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A Coresight PMU works the same way as any other PMU, i.e the name of the PMU is
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listed along with configuration options within forward slashes '/'. Since a
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Coresight system will typically have more than one sink, the name of the sink to
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work with needs to be specified as an event option. Names for sink to choose
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from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
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work with needs to be specified as an event option.
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On newer kernels the available sinks are listed in sysFS under:
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($SYSFS)/bus/event_source/devices/cs_etm/sinks/
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root@linaro-nano:~# ls /sys/bus/coresight/devices/
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20010000.etf 20040000.funnel 20100000.stm 22040000.etm
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22140000.etm 230c0000.funnel 23240000.etm 20030000.tpiu
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20070000.etr 20120000.replicator 220c0000.funnel
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23040000.etm 23140000.etm 23340000.etm
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root@localhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
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tmc_etf0 tmc_etr0 tpiu0
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root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program
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On older kernels, this may need to be found from the list of coresight devices,
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available under ($SYSFS)/bus/coresight/devices/:
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root:~# ls /sys/bus/coresight/devices/
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etm0 etm1 etm2 etm3 etm4 etm5 funnel0
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funnel1 funnel2 replicator0 stm0 tmc_etf0 tmc_etr0 tpiu0
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root@linaro-nano:~# perf record -e cs_etm/@tmc_etr0/u --per-thread program
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As mentioned above in section "Device Naming scheme", the names of the devices could
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look different from what is used in the example above. One must use the device names
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as it appears under the sysFS.
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The syntax within the forward slashes '/' is important. The '@' character
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tells the parser that a sink is about to be specified and that this is the sink
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@ -352,7 +404,7 @@ perf can be used to record and analyze trace of programs.
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Execution can be recorded using 'perf record' with the cs_etm event,
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specifying the name of the sink to record to, e.g:
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perf record -e cs_etm/@20070000.etr/u --per-thread
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perf record -e cs_etm/@tmc_etr0/u --per-thread
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The 'perf report' and 'perf script' commands can be used to analyze execution,
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synthesizing instruction and branch events from the instruction trace.
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@ -381,7 +433,7 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
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Bubble sorting array of 30000 elements
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5910 ms
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$ perf record -e cs_etm/@20070000.etr/u --per-thread taskset -c 2 ./sort
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$ perf record -e cs_etm/@tmc_etr0/u --per-thread taskset -c 2 ./sort
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Bubble sorting array of 30000 elements
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12543 ms
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[ perf record: Woken up 35 times to write data ]
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@ -405,7 +457,7 @@ than the program flow through the code.
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As with any other CoreSight component, specifics about the STM tracer can be
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found in sysfs with more information on each entry being found in [1]:
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root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
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root@genericarmv8:~# ls /sys/bus/coresight/devices/stm0
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enable_source hwevent_select port_enable subsystem uevent
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hwevent_enable mgmt port_select traceid
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root@genericarmv8:~#
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@ -413,14 +465,14 @@ root@genericarmv8:~#
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Like any other source a sink needs to be identified and the STM enabled before
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being used:
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root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink
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root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source
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root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/tmc_etf0/enable_sink
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root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/stm0/enable_source
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From there user space applications can request and use channels using the devfs
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interface provided for that purpose by the generic STM API:
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root@genericarmv8:~# ls -l /dev/20100000.stm
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crw------- 1 root root 10, 61 Jan 3 18:11 /dev/20100000.stm
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root@genericarmv8:~# ls -l /dev/stm0
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crw------- 1 root root 10, 61 Jan 3 18:11 /dev/stm0
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root@genericarmv8:~#
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Details on how to use the generic STM API can be found here [2].
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