Re: [PATCH 01/10] perf tools: Add fallback for exclude_guest

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Sep 06, 2024 at 09:47:53AM -0400, Liang, Kan wrote:
> 
> 
> On 2024-09-05 4:24 p.m., Namhyung Kim wrote:
> > Commit 7b100989b4f6bce70 ("perf evlist: Remove __evlist__add_default")
> > changed to parse "cycles:P" event instead of creating a new cycles
> > event for perf record.  But it also changed the way how modifiers are
> > handled so it doesn't set the exclude_guest bit by default.
> > 
> > It seems Apple M1 PMU requires exclude_guest set and returns EOPNOTSUPP
> > if not.  Let's add a fallback so that it can work with default events.
> > 
> > Fixes: 7b100989b4f6bce70 ("perf evlist: Remove __evlist__add_default")
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: James Clark <james.clark@linaro.org>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  tools/perf/builtin-stat.c |  3 +--
> >  tools/perf/util/evsel.c   | 21 +++++++++++++++++++++
> >  2 files changed, 22 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > index cf985cdb9a6ee588..d8315dae930184ba 100644
> > --- a/tools/perf/builtin-stat.c
> > +++ b/tools/perf/builtin-stat.c
> > @@ -639,8 +639,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
> >  	 * (behavior changed with commit b0a873e).
> >  	 */
> >  	if (errno == EINVAL || errno == ENOSYS ||
> > -	    errno == ENOENT || errno == EOPNOTSUPP ||
> > -	    errno == ENXIO) {
> > +	    errno == ENOENT || errno == ENXIO) {
> >  		if (verbose > 0)
> >  			ui__warning("%s event is not supported by the kernel.\n",
> >  				    evsel__name(counter));
> 
> It seems the behavior for other reasons which trigger the 'EOPNOTSUPP'
> is changed as well.
> At least, it looks like we don't skip the member event with EOPNOTSUPP
> anymore.
> 
> I'm not sure if it's a big deal. But I think we'd better mention it in
> the change log or the comments.

Yeah I think it should handle EOPNOTSUPP at the end of the function to
maintain the behavior.  Still it's not exactly the same but I think the
skippable case is ok.  Thanks for pointing this out.

Thanks,
Namhyung

> 
> > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > index 49cc71511c0c8ce8..d59ad76b28758906 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -3244,6 +3244,27 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> >  		evsel->core.attr.exclude_kernel = 1;
> >  		evsel->core.attr.exclude_hv     = 1;
> >  
> > +		return true;
> > +	} else if (err == EOPNOTSUPP && !evsel->core.attr.exclude_guest &&
> > +		   !evsel->exclude_GH) {
> > +		const char *name = evsel__name(evsel);
> > +		char *new_name;
> > +		const char *sep = ":";
> > +
> > +		/* Is there already the separator in the name. */
> > +		if (strchr(name, '/') ||
> > +		    (strchr(name, ':') && !evsel->is_libpfm_event))
> > +			sep = "";
> > +
> > +		if (asprintf(&new_name, "%s%sH", name, sep) < 0)
> > +			return false;
> > +
> > +		free(evsel->name);
> > +		evsel->name = new_name;
> > +		/* Apple M1 requires exclude_guest */
> > +		scnprintf(msg, msgsize, "trying to fall back to excluding guest samples");
> > +		evsel->core.attr.exclude_guest = 1;
> > +
> >  		return true;
> >  	}
> >