[PATCH] perf: test: Speed up running brstack test

["Rob Herring (Arm)" <robh@kernel.org>]

From: James Clark <james.clark@arm.com>

The brstack test runs quite slowly in software models. Part of the reason
is "xargs -n1" is quite inefficient in replacing spaces with newlines.
While that's not noticeable on normal machines, it is on software models.
Use "tr -s ' ' '\n'" instead which can do the same transformation, but is
much faster. For comparison on an M1 Macbook Pro:

$ time seq -s ' ' 10000 | xargs -n1 > /dev/null

real    0m2.729s
user    0m2.009s
sys     0m0.914s
$ time seq -s ' ' 10000 | tr -s ' ' '\n' | grep '.' > /dev/null

real    0m0.002s
user    0m0.001s
sys     0m0.001s

The "grep '.'" is also needed to remove any remaining blank lines.

Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
[robh: Drop changing loop iterations on arm64. Squash blank line fix and redo commit msg]
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
Originally part of this series[1], but I've dropped any Arm specifics, 
and it stands on its own. No reason this needs to wait on Arm BRBE 
support (which I'm working on now). I don't expect to have other changes 
to this test related to BRBE anymore.

[1] https://lore.kernel.org/all/20240613061731.3109448-8-anshuman.khandual@arm.com/

 tools/perf/tests/shell/test_brstack.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/tests/shell/test_brstack.sh b/tools/perf/tests/shell/test_brstack.sh
index 5f14d0cb013f..e01df7581393 100755
--- a/tools/perf/tests/shell/test_brstack.sh
+++ b/tools/perf/tests/shell/test_brstack.sh
@@ -30,7 +30,7 @@ test_user_branches() {
 	echo "Testing user branch stack sampling"
 
 	perf record -o $TMPDIR/perf.data --branch-filter any,save_type,u -- ${TESTPROG} > /dev/null 2>&1
-	perf script -i $TMPDIR/perf.data --fields brstacksym | xargs -n1 > $TMPDIR/perf.script
+	perf script -i $TMPDIR/perf.data --fields brstacksym | tr -s ' ' '\n' > $TMPDIR/perf.script
 
 	# example of branch entries:
 	# 	brstack_foo+0x14/brstack_bar+0x40/P/-/-/0/CALL
@@ -59,7 +59,7 @@ test_filter() {
 	echo "Testing branch stack filtering permutation ($test_filter_filter,$test_filter_expect)"
 
 	perf record -o $TMPDIR/perf.data --branch-filter $test_filter_filter,save_type,u -- ${TESTPROG} > /dev/null 2>&1
-	perf script -i $TMPDIR/perf.data --fields brstack | xargs -n1 > $TMPDIR/perf.script
+	perf script -i $TMPDIR/perf.data --fields brstack | tr -s ' ' '\n' | grep '.' > $TMPDIR/perf.script
 
 	# fail if we find any branch type that doesn't match any of the expected ones
 	# also consider UNKNOWN branch types (-)
-- 
2.45.2