linux-kernel - Re: [PATCH v1] perf test: Parse events workaround for dash/minus

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Date:   Thu, 13 Oct 2022 13:11:00 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        "Namhyung Kim" <namhyung@...nel.org>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v1] perf test: Parse events workaround for dash/minus

On 13/10/2022 02:12, Ian Rogers wrote:
> Skip an event configuration for event names with a dash/minus in them.
> Events with a dash/minus in their name cause parsing issues as legacy
> encoding of events would use a dash/minus as a separator. The parser
> separates events with dashes into prefixes and suffixes and then
> recombines them. Unfortunately if an event has part of its name that
> matches a legacy token then the recombining fails. This is seen for
> branch-brs where branch is a legacy token. branch-brs was introduced
> to sysfs in:
> https://lore.kernel.org/all/20220322221517.2510440-5-eranian@google.com/
> The failure is shown below as well as the workaround to use a config
> where the dash/minus isn't treated specially:
> 
> ```
> $ perf stat -e branch-brs true
> event syntax error: 'branch-brs'
>                             \___ parser error
> 
> $ perf stat -e cpu/branch-brs/ true
> 
>   Performance counter stats for 'true':
> 
>              46,179      cpu/branch-brs/
> ```
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>   tools/perf/tests/parse-events.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/tools/perf/tests/parse-events.c b/tools/perf/tests/parse-events.c
> index 459afdb256a1..3440dd2616b0 100644
> --- a/tools/perf/tests/parse-events.c
> +++ b/tools/perf/tests/parse-events.c
> @@ -2237,6 +2237,19 @@ static int test__pmu_events(struct test_suite *test __maybe_unused, int subtest
>   			pr_debug("Test PMU event failed for '%s'", name);
>   			ret = combine_test_results(ret, test_ret);
>   		

Hi Ian,

}
> +		/*
> +		 * Names containing '-' are recognized as prefixes and suffixes
> +		 * due to '-' being a legacy PMU separator. This fails when the
> +		 * prefix or suffix collides with an existing legacy token. For
> +		 * example, branch-brs has a prefix (branch) that collides with
> +		 * a PE_NAME_CACHE_TYPE token causing a parse error as a suffix
> +		 * isn't expected after this.

OK, so you want to skip anything with '-'. Will we now miss out on 
events which contain a '-' but don't clash with an existing legacy token?

>  As event names in the config
> +		 * slashes are allowed a '-' in the name we check this works
> +		 * above.

Sorry, I can't follow what you mean here. Do you mean that 
"cpu/branch-brs/" works ok and we continue to test it?

> +		 */
> +		if (strchr(ent->d_name, '-'))
> +			continue;

Thanks,
John

> +
>   		snprintf(name, sizeof(name), "%s:u,cpu/event=%s/u", ent->d_name, ent->d_name);
>   		e.name  = name;
>   		e.check = test__checkevent_pmu_events_mix;