From b861fd7e0efc4dc2376e7212f59a9b32d1383c00 Mon Sep 17 00:00:00 2001 From: Thomas Richter Date: Mon, 6 Nov 2023 10:16:27 +0100 Subject: [PATCH] perf tests offcpu: Adjust test case perf record offcpu profiling tests for s390 On s390 using linux-next the test case: 87: perf record offcpu profiling tests fails. The root cause is this command # ./perf record --off-cpu -e dummy -- ./perf bench sched messaging -l 10 # Running 'sched/messaging' benchmark: # 20 sender and receiver processes per group # 10 groups == 400 processes run Total time: 0.231 [sec] [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.077 MB perf.data (401 samples) ] # It does not generate 800+ sample entries, on s390 usually around 40[1-9], sometimes a few more, but never more than 450. The higher the number of CPUs the lower the number of samples. Looking at function chain: bench_sched_messaging() +--> group() the senders and receiver threads are created. The senders and receivers call function ready() which writes one bytes and wait for a reply using poll system() call. As context switches are counted, the function ready() will trigger a context switch when no input data is available after the write system call. The write system call does not trigger context switches when the data size is small. And writing 1000 bytes (10 iterations with 100 bytes) is not much and certainly won't block. The 400+ context switch on s390 occur when the some receiver/sender threads call ready() and wait for the response from function bench_sched_messaging() being kicked off. Lower the number of expected context switches to 400 to succeed on s390. Suggested-by: Namhyung Kim Signed-off-by: Ilya Leoshkevich Signed-off-by: Thomas Richter Acked-by: Namhyung Kim Cc: Heiko Carstens Cc: Sumanth Korikkar Cc: Sven Schnelle Cc: Vasily Gorbik Co-developed-by: Ilya Leoshkevich Link: https://lore.kernel.org/r/20231106091627.2022530-1-tmricht@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/tests/shell/record_offcpu.sh | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/perf/tests/shell/record_offcpu.sh b/tools/perf/tests/shell/record_offcpu.sh index a1ef8f0d2b5c..67c925f3a15a 100755 --- a/tools/perf/tests/shell/record_offcpu.sh +++ b/tools/perf/tests/shell/record_offcpu.sh @@ -77,9 +77,9 @@ test_offcpu_child() { err=1 return fi - # each process waits for read and write, so it should be more than 800 events + # each process waits at least for poll, so it should be more than 400 events if ! perf report -i ${perfdata} -s comm -q -n -t ';' --percent-limit=90 | \ - awk -F ";" '{ if (NF > 3 && int($3) < 800) exit 1; }' + awk -F ";" '{ if (NF > 3 && int($3) < 400) exit 1; }' then echo "Child task off-cpu test [Failed invalid output]" err=1