perf test brstack: Speed up running test by using tr -s instead of xargs

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>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241213231312.2640687-2-robh@kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
[robh: Drop changing loop iterations on arm64. Squash blank line fix and redo commit msg]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: James-A-Clark

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 (-)