Re: [PATCH 7/9] perf test cs-etm: Test branch history on existing samples

On 03/08/2026 10:06, Amir Ayupov wrote:

Add a CoreSight shell test for --itrace=L. Record timestamped ETM trace with explicit -T sample timestamps and AUX pause/resume events, then check that the pause samples carry both a multi-frame callchain and a non-empty branch stack for each of the workload's two processes.

Decode the same recording with L4 and L64 and reject any branch stack deeper than the requested depth.

The test skips when cs_etm is absent, when not run as root, or when the recording turns out to lack virtual timestamps. It exercises the timestamp-gated path and the requested-depth bound; it does not attempt to verify that the attached history is correlated to the sample.

Signed-off-by: Amir Ayupov aaupov@fb.com

.../tests/shell/coresight/add_last_branch.sh | 175 ++++++++++++++++++ 1 file changed, 175 insertions(+) create mode 100755 tools/perf/tests/shell/coresight/add_last_branch.sh

diff --git a/tools/perf/tests/shell/coresight/add_last_branch.sh b/tools/perf/tests/shell/coresight/add_last_branch.sh new file mode 100755 index 0000000000000..4654069ad651f --- /dev/null +++ b/tools/perf/tests/shell/coresight/add_last_branch.sh @@ -0,0 +1,175 @@ +#!/bin/bash -e +# SPDX-License-Identifier: GPL-2.0 +# CoreSight branch history on existing samples (exclusive)

+perf list pmu | grep -q 'cs_etm//' || exit 2

+if [ "$(id -u)" != 0 ]; then

• echo "[Skip] No root permission"
• exit 2

+fi

Is this so you can use -C 0? It's not completely obvious what that has to do with the test. Can you not drop the -C option or use --per-thread mode with a simpler non-forking workload?

I don't mind keeping it for some variety in the tests, but it should be documented.

+tmpdir=$(mktemp -d /tmp/perf-cs-add-last-branch.XXXXX)

+cleanup() +{

• rm -rf "$tmpdir"
• trap - EXIT TERM INT

+}

+# shellcheck disable=SC2317 # Called through trap. +trap_cleanup() +{

• cleanup
• exit 1

+} +trap trap_cleanup EXIT TERM INT

+record_data() +{

• if perf record -T -o "$tmpdir/data" -C 0 \

• -e cs_etm/aux-action=start-paused,timestamp/u \
  

Timestamp needs a value on newer kernels or Perf returns an error. But do you need to provide the option at all? It's on by default for per-CPU mode.

• -e cycles/aux-action=resume,period=550019/u \
  

• -e cycles/aux-action=pause,period=100003,call-graph=fp/u -- \
  

• taskset --cpu-list 0 perf test -w context_switch_loop 100000 \
  

The other Coresight tests use --workload-ctl to record less data and save some decode time. I think this test might benefit from it too.

• >/dev/null 2>"$tmpdir/stderr"; then
  

• return 0
  

• fi
• echo "Failed to record ETM trace with AUX pause/resume" >&2
• cat "$tmpdir/stderr" >&2
• return 1

+}

+decode() +{

• local size=$1
• local output=$2
• if perf script -i "$tmpdir/data" --itrace="L$size" \

• -F comm,pid,tid,event,ip,brstack >"$output" \
  

• 2>"$tmpdir/stderr"; then
  

• return 0
  

• fi
• if grep -q "itrace=L requires virtual timestamped trace" \

• "$tmpdir/stderr"; then
  

• echo "[Skip] Virtual CoreSight timestamps are not available"
  

• cleanup
  

• exit 2
  

• fi
• cat "$tmpdir/stderr" >&2
• return 1

+}

+check_process_samples() +{

• local output=$1
• local comm
• for comm in proc1 proc2; do

• awk -v comm="$comm" '
  

• 	$1 == comm && /cycles\/aux-action=pause/ {
  

• 		in_sample = 1
  

• 		next
  

• 	}
  

• 	!NF {
  

• 		in_sample = 0
  

• 		next
  

• 	}
  

• 	in_sample && /0x[[:xdigit:]]+\/0x[[:xdigit:]]+\// {
  

• 		found = 1
  

• 	}
  

• 	END { exit !found }
  

• ' "$output" || {
  

• 	echo "No pause-event branch stack found for $comm" >&2
  

• 	return 1
  

• }
  

• done

+}

+check_callchains() +{

• local output="$tmpdir/script-callchain"
• perf script -i "$tmpdir/data" -F comm,event,ip >"$output" 2>/dev/null
• awk '

• /cycles\/aux-action=pause/ {
  

• 	in_sample = 1
  

• 	frames = 0
  

• 	next
  

• }
  

• !NF {
  

• 	if (in_sample && frames >= 2)
  

• 		found = 1
  

• 	in_sample = 0
  

• 	next
  

• }
  

• in_sample && /^[[:space:]]+[[:xdigit:]]+([[:space:]]|$)/ {
  

• 	frames++
  

• }
  

• END {
  

• 	if (in_sample && frames >= 2)
  

• 		found = 1
  

• 	exit !found
  

• }
  

• ' "$output" || {

• echo "No multi-frame pause-event callchain found" >&2
  

• return 1
  

• }

Can you add some example output in the test saying what these awks are looking for. It failed for me but I wasn't sure why. I've attached my script-callchain file if that helps.

+}

+check_branch_stacks() +{

• local output=$1
• local max_entries=$2
• local ret
• if awk -v max="$max_entries" '

• /0x[[:xdigit:]]+\/0x[[:xdigit:]]+\// {
  

• 	entries = 0
  

• 	for (i = 1; i <= NF; i++)
  

• 		if ($i ~ /^0x[[:xdigit:]]+\/0x[[:xdigit:]]+\//)
  

• 			entries++
  

• 	if (entries)
  

• 		found = 1
  

• 	if (entries > max) {
  

• 		status = 2
  

• 		exit
  

• 	}
  

• }
  

• END {
  

• 	if (status)
  

• 		exit status
  

• 	if (!found)
  

• 		exit 1
  

• }
  

• ' "$output"; then

• return 0
  

• else

• ret=$?
  

• fi
• case $ret in
• 1. echo "No ETM branch stacks found" >&2 ;;
• 2. echo "Branch stack exceeds requested L$max_entries depth" >&2 ;;
• esac
• return 1

+}

+record_data +check_callchains

+decode 4 "$tmpdir/script-l4" +check_process_samples "$tmpdir/script-l4" +check_branch_stacks "$tmpdir/script-l4" 4

+decode 64 "$tmpdir/script-l64" +check_process_samples "$tmpdir/script-l64" +check_branch_stacks "$tmpdir/script-l64" 64

+cleanup +exit 0