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

[James Clark <james.clark@linaro.org>]

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