linux-kernel - Re: [PATCH] perf test: Add a perf event fallback test

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Message-ID: <aRPdmoNdUWIlWhJU@google.com>
Date: Tue, 11 Nov 2025 17:06:34 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Zide Chen <zide.chen@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Ian Rogers <irogers@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	thomas.falcon@...el.com, dapeng1.mi@...ux.intel.com,
	xudong.hao@...el.com
Subject: Re: [PATCH] perf test: Add a perf event fallback test

On Tue, Nov 11, 2025 at 02:42:46PM -0800, Zide Chen wrote:
> This adds test cases to verify the precise ip fallback logic:
> 
> - If the system supports precise ip, for an event given with the maximum
>   precision level, it should be able to decrease precise_ip to find a
>   supported level.
> - The same fallback behavior should also work in more complex scenarios,
>   such as event groups or when PEBS is involved
> 
> Additional fallback tests, such as those covering missing feature cases,
> can be added in the future.
> 
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> Signed-off-by: Zide Chen <zide.chen@...el.com>
> ---
>  .../tests/shell/test_event_open_fallback.sh   | 86 +++++++++++++++++++
>  1 file changed, 86 insertions(+)
>  create mode 100755 tools/perf/tests/shell/test_event_open_fallback.sh
> 
> diff --git a/tools/perf/tests/shell/test_event_open_fallback.sh b/tools/perf/tests/shell/test_event_open_fallback.sh
> new file mode 100755
> index 000000000000..72c1ac32c785
> --- /dev/null
> +++ b/tools/perf/tests/shell/test_event_open_fallback.sh
> @@ -0,0 +1,86 @@
> +#!/bin/bash
> +# Perf event open fallback test
> +# SPDX-License-Identifier: GPL-2.0
> +
> +skip_cnt=0
> +ok_cnt=0
> +err_cnt=0
> +
> +cleanup()
> +{
> +	rm -f perf.data
> +	rm -f perf.data.old
> +	trap - EXIT TERM INT
> +}
> +
> +trap_cleanup()
> +{
> +	cleanup
> +	exit 1
> +}
> +
> +trap trap_cleanup EXIT TERM INT
> +
> +perf_record()
> +{
> +	perf record "$@" -- true 1>/dev/null 2>&1
> +}
> +
> +test_decrease_precise_ip()
> +{
> +	echo "Decrease precise ip test"
> +
> +	perf list pmu | grep -q 'cycles' || return 2
> +
> +	if ! perf_record -e cycles; then
> +		return 2
> +	fi
> +
> +	# It should reduce precision level down to 0 if needed.
> +	if ! perf_record -e cycles:ppp; then

I think you need 'P' instead of 'ppp' for automatic precision.

Thanks,
Namhyung


> +		return 1
> +	fi
> +	return 0
> +}
> +
> +test_decrease_precise_ip_complicated()
> +{
> +	echo "Decrease precise ip test (complicated case)"
> +
> +	perf list pmu | grep -q 'mem-loads-aux' || return 2
> +
> +	if ! perf_record -e '{cpu/mem-loads-aux/S,cpu/mem-loads/PS}'; then
> +		return 1
> +	fi
> +	return 0
> +}
> +
> +count_result()
> +{
> +	if [ "$1" -eq 2 ] ; then
> +		skip_cnt=$((skip_cnt + 1))
> +		return
> +	fi
> +	if [ "$1" -eq 0 ] ; then
> +		ok_cnt=$((ok_cnt + 1))
> +		return
> +	fi
> +	err_cnt=$((err_cnt + 1))
> +}
> +
> +ret=0
> +test_decrease_precise_ip		|| ret=$? ; count_result $ret ; ret=0
> +test_decrease_precise_ip_complicated	|| ret=$? ; count_result $ret ; ret=0
> +
> +cleanup
> +
> +if [ ${err_cnt} -gt 0 ] ; then
> +	exit 1
> +fi
> +
> +if [ ${ok_cnt} -gt 0 ] ; then
> +	exit 0
> +fi
> +
> +# Skip
> +exit 2
> -- 
> 2.51.1
>