[PATCH v2 09/11] perf tests: Fix the Intel PT virtual LBR check

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

The record this check uses writes aux samples, and with the single data
page the other tests ask for they are lost:

  Warning: Processed 29 samples and lost 100.00%

so no branches are decoded and the check fails with "Failed with virtual
lbr".  Record with 4 data pages and 128 auxtrace pages: the same trace
decodes 64 branches and still fits the mlock budget.

Require the python perf module to provide session, not just to be
importable: a perf whose python bindings are not found can pick up an
unrelated module and fail with

  Error processing events: module 'perf' has no attribute 'session'

instead of skipping the subtest.

Detected building perf on fedora:44 on the runner with Intel PT hardware,
where the subtest failed with "Failed with virtual lbr" in the container,
and with the python error when run as root on the same machine.

Fixes: 915d6b14dc0c ("perf test: Migrate Intel PT virtual LBR test to Python API")
Signed-off-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/tests/shell/test_intel_pt.sh | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/perf/tests/shell/test_intel_pt.sh b/tools/perf/tests/shell/test_intel_pt.sh
index c0ecece0a8255124..511440b5956a6897 100755
--- a/tools/perf/tests/shell/test_intel_pt.sh
+++ b/tools/perf/tests/shell/test_intel_pt.sh
@@ -384,13 +384,14 @@ test_virtual_lbr()
 	# shellcheck source=lib/setup_python.sh
 	. "${shelldir}"/lib/setup_python.sh
 
-	if ! "$PYTHON" -c 'import perf' > /dev/null 2>&1; then
-		echo "SKIP: Python perf module not found"
+	if ! "$PYTHON" -c 'import perf; perf.session' > /dev/null 2>&1; then
+		echo "SKIP: Python perf module with session support not found"
 		return 2
 	fi
 
-	# Check if virtual lbr is working
-	perf_record_no_bpf -o "${tmpfile}" --aux-sample \
+	# Check if virtual lbr is working.  This records aux samples, which a
+	# single data page overruns, so give it more room than the other tests.
+	perf_record_no_bpf -m 4,128 -o "${tmpfile}" --aux-sample \
 		-e '{intel_pt//,cycles}:u' perf test -w brstack || return 1
 	perf inject --itrace=L -i "${tmpfile}" -o "${perfdatafile}" || return 1
 	output=$("$PYTHON" "${shelldir}/lib/perf_brstack_max.py" -i "${perfdatafile}") || return 1
-- 
2.56.0