linux-kernel - Re: [PATCH v1 2/3] perf arm-spe: Correct sample flags for dummy event

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Date:   Tue, 18 May 2021 09:54:02 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     James Clark <james.clark@....com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        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@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Al Grant <Al.Grant@....com>
Subject: Re: [PATCH v1 2/3] perf arm-spe: Correct sample flags for dummy event

Em Wed, May 12, 2021 at 11:23:30PM +0800, Leo Yan escreveu:
> On Wed, May 12, 2021 at 05:39:56PM +0300, James Clark wrote:
> > 
> > 
> > On 29/04/2021 18:00, Leo Yan wrote:
> > > The dummy event is mainly used for mmap, the TIME sample is only needed
> > > for per-cpu case so that the perf tool can rely on the correct timing
> > > for parsing symbols.  And the CPU sample is useless for mmap.
> > > 
> > > This patch enables TIME sample for per-cpu mmap and doesn't enable CPU
> > > sample.  For later extension (e.g. support multiple AUX events), it sets
> > > the dummy event when the condition "opts->full_auxtrace" is true.
> > > 
> > > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > > ---
> > >  tools/perf/arch/arm64/util/arm-spe.c | 30 ++++++++++++++++------------
> > >  1 file changed, 17 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/tools/perf/arch/arm64/util/arm-spe.c b/tools/perf/arch/arm64/util/arm-spe.c
> > > index 902e73a64184..f6eec0900604 100644
> > > --- a/tools/perf/arch/arm64/util/arm-spe.c
> > > +++ b/tools/perf/arch/arm64/util/arm-spe.c
> > > @@ -70,7 +70,6 @@ static int arm_spe_recording_options(struct auxtrace_record *itr,
> > >  	struct evsel *evsel, *arm_spe_evsel = NULL;
> > >  	struct perf_cpu_map *cpus = evlist->core.cpus;
> > >  	bool privileged = perf_event_paranoid_check(-1);
> > > -	struct evsel *tracking_evsel;
> > >  	int err;
> > >  
> > >  	sper->evlist = evlist;
> > > @@ -126,18 +125,23 @@ static int arm_spe_recording_options(struct auxtrace_record *itr,
> > >  		evsel__set_sample_bit(arm_spe_evsel, CPU);
> > >  
> > >  	/* Add dummy event to keep tracking */
> > > -	err = parse_events(evlist, "dummy:u", NULL);
> > > -	if (err)
> > > -		return err;
> > > -
> > > -	tracking_evsel = evlist__last(evlist);
> > > -	evlist__set_tracking_event(evlist, tracking_evsel);
> > > -
> > > -	tracking_evsel->core.attr.freq = 0;
> > > -	tracking_evsel->core.attr.sample_period = 1;
> > > -	evsel__set_sample_bit(tracking_evsel, TIME);
> > > -	evsel__set_sample_bit(tracking_evsel, CPU);
> > > -	evsel__reset_sample_bit(tracking_evsel, BRANCH_STACK);
> > > +	if (opts->full_auxtrace) {
> > > +		struct evsel *tracking_evsel;
> > 
> > Hi Leo,
> > 
> > I know the "if (opts->full_auxtrace)" pattern is copied from other auxtrace
> > files, but I don't think it does anything because there is this at the top
> > of the function:
> > 
> >    	if (!opts->full_auxtrace)
> > 		return 0;
> > 
> > The same applies for other usages of "full_auxtrace" in the same function.
> > They are all always true. I'm also not sure if it's ever defined what
> > full_auxtrace means.
> 
> Good pointing.  TBH, I also stuggled for handling "opts->full_auxtrace"
> when wrote the patch; IIUC, "opts->full_auxtrace" is also used in
> builtin-record.c to indicate if the recording contains AUX tracing.
> 
> Will follow your suggestion to respin the patch (and refine the code)
> to remove the redundant condition checking for "opts->full_auxtrace".

Ok, so please collect his Tested-by and Reviewed-by and I'll wait for v2
then,

- Arnaldo