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

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

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