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

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Date:   Fri, 28 Oct 2022 10:55:14 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     John Garry <john.garry@...wei.com>
Cc:     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 Mon, Oct 17, 2022 at 4:07 PM Ian Rogers <irogers@...gle.com> wrote:
>
> On Thu, Oct 13, 2022 at 5:11 AM John Garry <john.garry@...wei.com> wrote:
> >
> > 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?
>
> Yes. The long term solution here is to ditch the current parse event
> code and its legacy support. An idea is to create a simplified parser
> as part of libperf2 (libperf but with a libbpf style license), use the
> new parser for metrics and events. In the events case, if the new
> parser fails then use the legacy parser and its weird handling of
> dashes.
>
> > >  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?
>
> Yep, as shown in the commit message. The comment isn't great, it
> should be worded something like:
>
> If an event name is in the config slashes, such as cpu/branch-brs/,  a
> '-' in the name works as the dash doesn't separate the parts of the
> name. This continues to be tested above.

Ping. It'd be nice to merge this as otherwise we have a perf test
failure on AMD.

Thanks,
Ian

> > > +              * above.
>
> Thanks,
> Ian
>
> > > +              */
> > > +             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;
> >