Re: [PATCH 24/25] perf test: Add CoreSight AUX sample decoding test

On 15/09/2026 16:49, Leo Yan wrote:

Add a shell test that records the brstack workload with 8 KiB AUX samples attached to cycle events. Pin the workload to a CPU with a TRBE sink and use per-thread recording with trace timestamps and context IDs disabled, exercising decoding with the owning sample's context.

Check branch stacks and callchains with --itrace=L4, L64, G3 and G3L64. Require at least one sample to reach both requested depths, with all callchain frames belonging to the workload, and reject samples exceeding either limit. Use a callchain depth of three to match the nested calls in brstack.

Compare with AUX decoding enabled and disabled to verify that adding history preserves the original PMU samples.

Assisted-by: Codex:gpt-6 Signed-off-by: Leo Yan leo.yan@arm.com

---

tools/perf/tests/shell/coresight/aux_sample.sh | 189 +++++++++++++++++++++++++ 1 file changed, 189 insertions(+)

diff --git a/tools/perf/tests/shell/coresight/aux_sample.sh b/tools/perf/tests/shell/coresight/aux_sample.sh new file mode 100755 index 0000000000000000000000000000000000000000..887ad6a085eacdfd192db3863fbb61dae1aa19b5 --- /dev/null +++ b/tools/perf/tests/shell/coresight/aux_sample.sh @@ -0,0 +1,189 @@ +#!/bin/bash -e +# SPDX-License-Identifier: GPL-2.0 +# CoreSight AUX samples with callchains and branch stacks (exclusive)

+export LC_ALL=C

+skip() +{

• echo "[Skip] $1"
• exit 2

+}

+perf list pmu | grep -q 'cs_etm//' || skip "cs_etm is not available" +perf check feature -q libopencsd || skip "perf was built without OpenCSD" +[ "$(id -u)" = 0 ] || skip "No root permission" +command -v taskset >/dev/null || skip "taskset is not available"

+# AUX sample now supports per CPU sink (e.g., TRBE). Select a usable CPU +# and name its sink explicitly to avoid a shared sink. +sink= +for dev in /sys/bus/coresight/devices/trbe[0-9]*; do

• [ -d "$dev" ] || continue
• name=${dev##*/}
• cpu=${name#trbe}
• [ -e "/sys/bus/event_source/devices/cs_etm/cpu$cpu" ] || continue
• if taskset -c "$cpu" true 2>/dev/null; then

• sink=$name
  

• break
  

• fi

+done +[ -n "$sink" ] || skip "No usable TRBE CPU is available"

+tmpdir=$(mktemp -d /tmp/perf-cs-aux-sample.XXXXXX)

+cleanup() +{

• rm -rf "$tmpdir"

+}

+trap cleanup EXIT +trap 'exit 1' TERM INT

+fail() +{

• echo "$1" >&2
• cat "$tmpdir/stderr" >&2
• exit 1

+}

+cf="$tmpdir/ctl" +af="$tmpdir/ack" +mkfifo "$cf" "$af"

+# Disable trace timestamps and context IDs to use the owning sample's context. +# Use a per-thread mmap so the explicit sink is only used on the pinned CPU. +if ! taskset -c "$cpu" perf record -o "$tmpdir/data" --aux-sample=8192 \

• -e "{cs_etm/@$sink,timestamp=0,contextid=0/u,cycles/period=100003/u}" \
• --per-thread -D -1 --control fifo:"$cf","$af" -- \

Minor nit, but on "[PATCH 00/14] perf cs-etm: Per-thread mode fixes and snapshot wrap support" I just did:

+if ! ls /sys/bus/coresight/devices/trbe* > /dev/null 2>&1; then + echo "No TRBE sinks, skipping output validation" + exit 0 +fi

I know looking up the actual sink, passing it in and also using --per-thread mode is "technically correct", but I think we can assume that any normal record command will work on any system with TRBE.

Otherwise, we should re-write all of the tests to only target CPUs with known loaded ETM instances instead of hard coding CPU 0 etc.

Other than that LGTM:

Reviewed-by: James Clark james.clark@linaro.org

• perf test --record-ctl fifo:"$cf","$af" -w brstack 1000000 \
• ...

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

• # Kernels without snapshot_aux reject the sampling event at open time.
• if grep -Eq 'sys_perf_event_open.*event (.*cycles.*): Invalid argument' \

• "$tmpdir/stderr"; then
  

• skip "Kernel does not accept CoreSight AUX sampling"
  

• fi
• fail "Failed to record CoreSight AUX samples"

+fi

+perf evlist -v -i "$tmpdir/data" >"$tmpdir/evlist" 2>"$tmpdir/stderr" ||

• fail "Failed to read AUX sample attributes"

+grep -Eq 'sample_type:.*|AUX(,||).*aux_sample_size: 8192(,|$)' \

• "$tmpdir/evlist" || fail "Missing AUX sample attributes"

+check_history() +{

• local options=$1
• local max_branches=$2
• local max_callchains=$3
• local output="$tmpdir/script-$options"
• perf script -i "$tmpdir/data" --itrace="$options" \

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

• 2>"$tmpdir/stderr" || fail "Failed to decode AUX samples with $options"
  

• # Some windows may contain incomplete trace. Require at least one cycle
• # sample to reach both requested depths, and reject any that exceed them.
• if ! awk -v max_branches="$max_branches" \

• -v max_callchains="$max_callchains" '
  

• function check_sample() {
  

• 	if (in_sample == 0) {
  

• 		return
  

• 	}
  

• 	if (branch_entries > max_branches || callchain_frames > max_callchains) {
  

• 		depth_exceeded = 1
  

• 	}
  

• 	# Both depths must be reached in the same sample, with all
  

• 	# callchain frames belonging to the brstack workload.
  

• 	if (branch_entries == max_branches &&
  

• 	    callchain_frames == max_callchains &&
  

• 	    workload_frames == max_callchains) {
  

• 		found_sample = 1
  

• 	}
  

• 	branch_entries = 0
  

• 	callchain_frames = 0
  

• 	workload_frames = 0
  

• 	in_sample = 0
  

• }
  

• {
  

• 	# A blank line marks the end of a sample.
  

• 	if (NF == 0) {
  

• 		check_sample()
  

• 		next
  

• 	}
  

• 	# Sample header: comm pid/tid [cpu] event ...
  

• 	# The event may include a PMU prefix and configuration terms.
  

• 	if ($4 ~ /(^|\/)cycles([,\/:]|$)/) {
  

• 		check_sample()
  

• 		in_sample = 1
  

• 	}
  

• 	if (in_sample == 0) {
  

• 		next
  

• 	}
  

• 	# Each branch entry is a field in 0xFROM/0xTO/... form.
  

• 	for (i = 1; i <= NF; i++) {
  

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

• 			branch_entries++
  

• 		}
  

• 	}
  

• 	# Callchain rows start with a hexadecimal IP, then a symbol.
  

• 	if ($1 ~ /^[[:xdigit:]]+$/) {
  

• 		callchain_frames++
  

• 		if ($2 ~ /^brstack(_|$)/) {
  

• 			workload_frames++
  

• 		}
  

• 	}
  

• }
  

• END {
  

• 	# Account for the last sample even without a trailing blank line.
  

• 	check_sample()
  

• 	if (depth_exceeded != 0) {
  

• 		print "AUX sample history exceeds the requested depth" > "/dev/stderr"
  

• 		exit 1
  

• 	}
  

• 	if (found_sample == 0) {
  

• 		printf "No sample has %d branches and %d workload callchain frames\n", \
  

• 			max_branches, max_callchains > "/dev/stderr"
  

• 		exit 1
  

• 	}
  

• 	exit 0
  

• }
  

• ' "$output"; then

• head -n 80 "$output" >&2
  

• fail "Missing AUX sample history or incorrect depth with $options"
  

• fi

+}

+check_sample_identity() +{

• local fields=comm,pid,tid,cpu,event,ip
• # Hiding history must leave exactly the original PMU samples, including
• # their PID/TID, CPU and sampled IP, with no synthesized events. Per-thread
• # recording does not require sample timestamps.
• perf script -i "$tmpdir/data" --no-itrace -F "$fields" \

• >"$tmpdir/original" 2>"$tmpdir/stderr" || fail "Failed to read cycle samples"
  

• perf script -i "$tmpdir/data" --itrace=L4 -F "$fields" \

• >"$tmpdir/decoded" 2>"$tmpdir/stderr" || fail "Failed to decode cycle samples"
  

• diff -u "$tmpdir/original" "$tmpdir/decoded" ||

• fail "AUX decoding changed the original cycle samples"
  

+}

+check_history L4 4 0 +check_history L64 64 0

+# brstack -> brstack_bench -> brstack_foo -> brstack_bar provides three +# nested calls whose caller frames can be reconstructed from an AUX window. +check_history G3 0 3 +check_history G3L64 64 3

+check_sample_identity

+echo "CoreSight AUX sample decoding: PASS"