linux-kernel - Re: [PATCH v3] perf evsel: Fix missing exclude

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Date:   Wed, 3 Nov 2021 08:32:14 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH v3] perf evsel: Fix missing exclude_{host,guest} setting

Em Wed, Nov 03, 2021 at 12:44:12AM -0700, Stephane Eranian escreveu:
> On Wed, Nov 3, 2021 at 12:24 AM Jiri Olsa <jolsa@...hat.com> wrote:
> > On Tue, Nov 02, 2021 at 04:21:21PM -0700, Namhyung Kim wrote:
> > > On Tue, Nov 2, 2021 at 7:10 AM Jiri Olsa <jolsa@...hat.com> wrote:
> > > > we were discussing this with Arnaldo yesterday and he had an idea to use
> > > > evsel->pmu link to store this info instead of hash.. I first thought we
> > > > needed 'evsel' related data, but after I gave it some thought I think that
> > > > might actually work

> > > I don't get it.. do we have evsel->pmu already?  Or do you want to add it?
> > > Yeah, the filtering facility (attr.exclude_*) should be kept in a PMU data
> > > not in the evsel.  So I added a hashmap to find the pmu data from attr.type.
> > > How do I use evsel->pmu to store the info then?

> > evsel->pmu is not there yet (only evsel->pmu_name) so that
> > would need to be added.. we have evsel__find_pmu available

> > then the idea is to use evsel->pmu instead of the hasmap,
> > like add:

> >   struct pmu {
> >     ...
> >     bool missing_exclude_guest;
> >   };

yeah, or more generaly:

	struct pmu {
		...
		struct {
			bool exclude_guess;
		} missing_features;
	};

> > set it when the guest filtering fails and and check it
> > instead of the hashmap__find call

> > > > my argument was following usecase:

> > > >   cycles:G,instructions:G,pmu/bla1/:G,pmu/bla2/

> > > > that we would falsely clear pmu/bla1/:G if we used the 'evsel->pmu' data..
> > > > but then I realized it's detection if pmu support :G and so if the :G is
> > > > not there, none of the events should have it

> > > > thoughts?

> > > I don't think I'm following well... ;-p

> > > If the pmu doesn't support host/guest filtering, pmu/bla1/G
> > > may count something.  Not sure if it's better to error out.
> > > But the cycles:G and instructions:G should result in 0
> > > in case there's no VM running.

> > hm, I think if pmu doesn't support host/guest filtering then
> > I think 'pmu/bla1/G' should error, no? better no number than
> > bad number

> Yes, it should in my opinion.

Yeah, I thought about this yesterday (holiday here).

- Arnaldo