linux-kernel - Re: [PATCH] perf parse-events: Set default GH modifier properly

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Message-ID: <CAP-5=fVoQXwFFdqY7ne0ZLJk+aTzm9knHqgVbvhJtb44doqe-g@mail.gmail.com>
Date: Fri, 6 Jun 2025 16:50:13 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Kan Liang <kan.liang@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf parse-events: Set default GH modifier properly

On Fri, Jun 6, 2025 at 3:54 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Commit 7b100989b4f6bce7 ("perf evlist: Remove __evlist__add_default")
> changed to use "cycles:P" as a default event.  But the problem is it
> cannot set other default modifiers correctly.
>
> perf kvm needs to set attr.exclude_host by default but it didn't work
> because of the logic in the parse_events__modifier_list().  Also the
> exclude_GH_default was applied only if ":u" modifier was specified -
> which is strange.  Move it out after handling the ":GH" and check
> perf_host and perf_guest properly.
>
> Before:
>   $ ./perf kvm record -vv true |& grep exclude
>   (nothing)
>
> But specifying an event (without a modifier) works:
>
>   $ ./perf kvm record -vv -e cycles true |& grep exclude
>     exclude_host                     1
>
> After:
> It now works for the both cases:
>
>   $ ./perf kvm record -vv true |& grep exclude
>     exclude_host                     1
>
>   $ ./perf kvm record -vv -e cycles true |& grep exclude
>     exclude_host                     1
>
> Fixes: 35c8d21371e9b342 ("perf tools: Don't set attr.exclude_guest by default")
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Code is more understandable than before and reads as correct.

Reviewed-by: Ian Rogers <irogers@...gle.com>

Perhaps consider adding test coverage in tools/perf/tests/parse-events.c ?

Thanks,
Ian

> ---
>  tools/perf/util/parse-events.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 7f34e602fc080881..d1965a7b97ed6b97 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -1830,13 +1830,11 @@ static int parse_events__modifier_list(struct parse_events_state *parse_state,
>                 int eH = group ? evsel->core.attr.exclude_host : 0;
>                 int eG = group ? evsel->core.attr.exclude_guest : 0;
>                 int exclude = eu | ek | eh;
> -               int exclude_GH = group ? evsel->exclude_GH : 0;
> +               int exclude_GH = eG | eH;
>
>                 if (mod.user) {
>                         if (!exclude)
>                                 exclude = eu = ek = eh = 1;
> -                       if (!exclude_GH && !perf_guest && exclude_GH_default)
> -                               eG = 1;
>                         eu = 0;
>                 }
>                 if (mod.kernel) {
> @@ -1859,6 +1857,13 @@ static int parse_events__modifier_list(struct parse_events_state *parse_state,
>                                 exclude_GH = eG = eH = 1;
>                         eH = 0;
>                 }
> +               if (!exclude_GH && exclude_GH_default) {
> +                       if (perf_host)
> +                               eG = 1;
> +                       else if (perf_guest)
> +                               eH = 1;
> +               }
> +
>                 evsel->core.attr.exclude_user   = eu;
>                 evsel->core.attr.exclude_kernel = ek;
>                 evsel->core.attr.exclude_hv     = eh;
> --
> 2.50.0.rc0.604.gd4ff7b7c86-goog
>