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>
This commit is contained in:
Suzuki K Poulose 2019-06-10 19:02:42 +01:00 committed by Jonathan Corbet
parent 83e8b971f8
commit cd84d63a29
1 changed files with 67 additions and 15 deletions

View File

@ -188,6 +188,49 @@ specific to that component only. "Implementation defined" customisations are
expected to be accessed and controlled using those entries.
Device Naming scheme
------------------------
The devices that appear on the "coresight" bus were named the same as their
parent devices, i.e, the real devices that appears on AMBA bus or the platform bus.
Thus the names were based on the Linux Open Firmware layer naming convention,
which follows the base physical address of the device followed by the device
type. e.g:
root:~# 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
However, with the introduction of ACPI support, the names of the real
devices are a bit cryptic and non-obvious. Thus, a new naming scheme was
introduced to use more generic names based on the type of the device. The
following rules apply:
1) Devices that are bound to CPUs, are named based on the CPU logical
number.
e.g, ETM bound to CPU0 is named "etm0"
2) All other devices follow a pattern, "<device_type_prefix>N", where :
<device_type_prefix> - A prefix specific to the type of the device
N - a sequential number assigned based on the order
of probing.
e.g, tmc_etf0, tmc_etr0, funnel0, funnel1
Thus, with the new scheme the devices could appear as :
root:~# ls /sys/bus/coresight/devices/
etm0 etm1 etm2 etm3 etm4 etm5 funnel0
funnel1 funnel2 replicator0 stm0 tmc_etf0 tmc_etr0 tpiu0
Some of the examples below might refer to old naming scheme and some
to the newer scheme, to give a confirmation that what you see on your
system is not unexpected. One must use the "names" as they appear on
the system under specified locations.
How to use the tracer modules
-----------------------------
@ -326,16 +369,25 @@ 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 ($SYSFS)/bus/coresight/devices:
work with needs to be specified as an event option.
On newer kernels the available sinks are listed in sysFS under:
($SYSFS)/bus/event_source/devices/cs_etm/sinks/
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@localhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
tmc_etf0 tmc_etr0 tpiu0
root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program
On older kernels, this may need to be found from the list of coresight devices,
available under ($SYSFS)/bus/coresight/devices/:
root:~# ls /sys/bus/coresight/devices/
etm0 etm1 etm2 etm3 etm4 etm5 funnel0
funnel1 funnel2 replicator0 stm0 tmc_etf0 tmc_etr0 tpiu0
root@linaro-nano:~# perf record -e cs_etm/@tmc_etr0/u --per-thread program
As mentioned above in section "Device Naming scheme", the names of the devices could
look different from what is used in the example above. One must use the device names
as it appears under the sysFS.
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
@ -352,7 +404,7 @@ perf can be used to record and analyze trace of programs.
Execution can be recorded using 'perf record' with the cs_etm event,
specifying the name of the sink to record to, e.g:
perf record -e cs_etm/@20070000.etr/u --per-thread
perf record -e cs_etm/@tmc_etr0/u --per-thread
The 'perf report' and 'perf script' commands can be used to analyze execution,
synthesizing instruction and branch events from the instruction trace.
@ -381,7 +433,7 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
Bubble sorting array of 30000 elements
5910 ms
$ perf record -e cs_etm/@20070000.etr/u --per-thread taskset -c 2 ./sort
$ perf record -e cs_etm/@tmc_etr0/u --per-thread taskset -c 2 ./sort
Bubble sorting array of 30000 elements
12543 ms
[ perf record: Woken up 35 times to write data ]
@ -405,7 +457,7 @@ 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
root@genericarmv8:~# ls /sys/bus/coresight/devices/stm0
enable_source hwevent_select port_enable subsystem uevent
hwevent_enable mgmt port_select traceid
root@genericarmv8:~#
@ -413,14 +465,14 @@ 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
root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/tmc_etf0/enable_sink
root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/stm0/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:~# ls -l /dev/stm0
crw------- 1 root root 10, 61 Jan 3 18:11 /dev/stm0
root@genericarmv8:~#
Details on how to use the generic STM API can be found here [2].