linux-kernel - Re: [PATCH v2] perf report: Set PERF_SAMPLE_DATA

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Message-ID: <YlgLGb+NkMNKc3+0@kernel.org>
Date:   Thu, 14 Apr 2022 08:52:57 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     James Clark <james.clark@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        German Gomez <german.gomez@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf report: Set PERF_SAMPLE_DATA_SRC bit for Arm SPE
 event

Em Thu, Apr 14, 2022 at 07:01:24PM +0800, Leo Yan escreveu:
> On Thu, Apr 14, 2022 at 11:29:48AM +0100, James Clark wrote:
> > On 14/04/2022 02:27, Arnaldo Carvalho de Melo wrote:
> > > Em Wed, Apr 13, 2022 at 05:23:17PM +0800, Leo Yan escreveu:
> > >> Since commit bb30acae4c4d ("perf report: Bail out --mem-mode if mem info
> > >> is not available") "perf mem report" and "perf report --mem-mode"
> > >> don't report result if the PERF_SAMPLE_DATA_SRC bit is missed in sample
> > >> type.
> > >>
> > >> The commit ffab48705205 ("perf: arm-spe: Fix perf report --mem-mode")
> > >> partially fixes the issue.  It adds PERF_SAMPLE_DATA_SRC bit for Arm SPE
> > >> event, this allows the perf data file generated by kernel v5.18-rc1 or
> > >> later version can be reported properly.
> > >>
> > >> On the other hand, perf tool still fails to be backward compatibility
> > >> for a data file recorded by an older version's perf which contains Arm
> > >> SPE trace data.  This patch is a workaround in reporting phase, when
> > >> detects ARM SPE PMU event and without PERF_SAMPLE_DATA_SRC bit, it will
> > >> force to set the bit in the sample type and give a warning info.
> > >>
> > >> Fixes: bb30acae4c4d ("perf report: Bail out --mem-mode if mem info is not available")
> > >> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > >> Tested-by: German Gomez <german.gomez@....com>
> > >> ---
> > >> v2: Change event name from "arm_spe_" to "arm_spe";
> > >>     Add German's test tag.
> > > 
> > > Tentatively applied, would be great to have James' and Ravi's
> > > Acked-by/Reviewed-by, which I'll add before pushing this out if provided
> > > in time.
> > > 
> > > - Arnaldo
> > >  
> > >>  tools/perf/builtin-report.c | 16 ++++++++++++++++
> > >>  1 file changed, 16 insertions(+)
> > >>
> > >> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > >> index 1ad75c7ba074..acb07a4a9b67 100644
> > >> --- a/tools/perf/builtin-report.c
> > >> +++ b/tools/perf/builtin-report.c
> > >> @@ -353,6 +353,7 @@ static int report__setup_sample_type(struct report *rep)
> > >>  	struct perf_session *session = rep->session;
> > >>  	u64 sample_type = evlist__combined_sample_type(session->evlist);
> > >>  	bool is_pipe = perf_data__is_pipe(session->data);
> > >> +	struct evsel *evsel;
> > >>  
> > >>  	if (session->itrace_synth_opts->callchain ||
> > >>  	    session->itrace_synth_opts->add_callchain ||
> > >> @@ -407,6 +408,21 @@ static int report__setup_sample_type(struct report *rep)
> > >>  	}
> > >>  
> > >>  	if (sort__mode == SORT_MODE__MEMORY) {
> > >> +		/*
> > >> +		 * FIXUP: prior to kernel 5.18, Arm SPE missed to set
> > >> +		 * PERF_SAMPLE_DATA_SRC bit in sample type.  For backward
> > >> +		 * compatibility, set the bit if it's an old perf data file.
> > >> +		 */
> > >> +		evlist__for_each_entry(session->evlist, evsel) {
> > >> +			if (strstr(evsel->name, "arm_spe") &&
> > >> +				!(sample_type & PERF_SAMPLE_DATA_SRC)) {
> > >> +				ui__warning("PERF_SAMPLE_DATA_SRC bit is not set "
> > >> +					    "for Arm SPE event.\n");
> > 
> > Looks ok to me. Personally I would remove the warning, otherwise people are going to start
> > thinking that they need to do something about it or something bad has happened.
> > 
> > But because we've fixed it up there shouldn't really need to be a warning or any action.
> 
> Understand.  The warning is not bad for developers but it might
> introduce confusion for users, and if we really want to check the sample
> type then we can use 'perf evlist' command, so it's not very useful for
> the warning.
> 
> I will remove the warning and resend a new patch.

Waiting then
 
> > I don't feel too strongly about this though, so I will leave it up to Leo to make the
> > final decision:
> > 
> > Reviewed-by: James Clark <james.clark@....com>
> 
> Thanks a lot for reviewing.
> Leo

-- 

- Arnaldo