[PATCH] perf/tests: Fix test case 95 on s390 and use same event

[Thomas Richter]

On linux-next tree perf test 95 was added recently.
s390 does not support branch sampling at all and the test case fails
despite for checking branch support before hand.
The check for support of branching
uses the software event named dummy, as seen in the line:

 perf record -b -o- -e dummy -B true > /dev/null 2>&1 || exit 2

However when the branch recording is actually done, a different
event is used, as seen in the line:

 perf record -o $TMPDIR/... --branch-filter any,save_type,u -- ...

The event is omitted and for perf record the default event is
cycles, which is not supported by s390 and this fails when executed
on s390:

 # perf record --branch-filter any,save_type,u -- \
	/tmp/__perf_test.program.iDSmQ/a.out
 Error:
 cycles: PMU Hardware or event type doesn't support branch stack sampling.
 #

Therefore fix this and use the same event cycles for testing support
and actually running the test.

Output before:
 # ./perf test -Fv 95
 95: Check branch stack sampling                                     :
 --- start ---
 Testing user branch stack sampling
 ---- end ----
 Check branch stack sampling: FAILED!
 #

Output after:
 # ./perf test -Fv 95
 95: Check branch stack sampling                                     :
 --- start ---
 ---- end ----
 Check branch stack sampling: Skip
 #

Fixes: b55878c90ab9 ("perf test: Add test for branch stack sampling")
Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
---
 tools/perf/tests/shell/test_brstack.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/tests/shell/test_brstack.sh b/tools/perf/tests/shell/test_brstack.sh
index 113ccd17bf03..c644f94a6500 100755
--- a/tools/perf/tests/shell/test_brstack.sh
+++ b/tools/perf/tests/shell/test_brstack.sh
@@ -12,7 +12,7 @@ if ! [ -x "$(command -v cc)" ]; then
 fi
 
 # skip the test if the hardware doesn't support branch stack sampling
-perf record -b -o- -e dummy -B true > /dev/null 2>&1 || exit 2
+perf record -b -o- -B true > /dev/null 2>&1 || exit 2
 
 TMPDIR=$(mktemp -d /tmp/__perf_test.program.XXXXX)
 
-- 
2.36.1