From: Robert Walker robert.walker@arm.com

Add notes on using perf to collect and analyze CoreSight trace

Signed-off-by: Robert Walker robert.walker@arm.com Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: coresight@lists.linaro.org Cc: linux-arm-kernel@lists.infradead.org Link: http://lkml.kernel.org/r/1518607481-4059-4-git-send-email-robert.walker@arm.... Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com --- Documentation/trace/coresight.txt | 51 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+)

diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt index a33c88cd5d1d..6f0120c3a4f1 100644 --- a/Documentation/trace/coresight.txt +++ b/Documentation/trace/coresight.txt @@ -330,3 +330,54 @@ 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 + + +Using perf tools +---------------- + +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 + +The 'perf report' and 'perf script' commands can be used to analyze execution, +synthesizing instruction and branch events from the instruction trace. +'perf inject' can be used to replace the trace data with the synthesized events. +The --itrace option controls the type and frequency of synthesized events +(see perf documentation). + +Note that only 64-bit programs are currently supported - further work is +required to support instruction decode of 32-bit Arm programs. + + +Generating coverage files for Feedback Directed Optimization: AutoFDO +--------------------------------------------------------------------- + +'perf inject' accepts the --itrace option in which case tracing data is +removed and replaced with the synthesized events. e.g. + + perf inject --itrace --strip -i perf.data -o perf.data.new + +Below is an example of using ARM ETM for autoFDO. It requires autofdo +(https://github.com/google/autofdo) and gcc version 5. The bubble +sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial). + + $ gcc-5 -O3 sort.c -o sort + $ taskset -c 2 ./sort + Bubble sorting array of 30000 elements + 5910 ms + + $ perf record -e cs_etm/@20070000.etr/u --per-thread taskset -c 2 ./sort + Bubble sorting array of 30000 elements + 12543 ms + [ perf record: Woken up 35 times to write data ] + [ perf record: Captured and wrote 69.640 MB perf.data ] + + $ perf inject -i perf.data -o inj.data --itrace=il64 --strip + $ create_gcov --binary=./sort --profile=inj.data --gcov=sort.gcov -gcov_version=1 + $ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo + $ taskset -c 2 ./sort_autofdo + Bubble sorting array of 30000 elements + 5806 ms