linux-kernel - Re: [PATCH v4 4/6] perf arm-spe: Assign kernel time to synthesized event

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Date:   Thu, 29 Apr 2021 23:23:26 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Al Grant <Al.Grant@....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>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] perf arm-spe: Assign kernel time to synthesized
 event

Hi James,

On Fri, Apr 16, 2021 at 03:51:25PM +0300, James Clark wrote:

[...]

> >>> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> >>> index 23714cf0380e..c13a89f06ab8 100644
> >>> --- a/tools/perf/util/arm-spe.c
> >>> +++ b/tools/perf/util/arm-spe.c
> >>> @@ -234,7 +234,7 @@ static void arm_spe_prep_sample(struct arm_spe *spe,
> >>>  	struct arm_spe_record *record = &speq->decoder->record;
> >>>  
> >>>  	if (!spe->timeless_decoding)
> >>> -		sample->time = speq->timestamp;
> >>> +		sample->time = tsc_to_perf_time(record->timestamp, &spe->tc);
> >>
> >>
> >> I noticed that in arm_spe_recording_options() the TIME sample bit is set regardless of any options.
> >> I don't know of a way to remove this, and if there isn't, does that mean that all the code in this
> >> file that looks at spe->timeless_decoding is untested and has never been hit?
> >>
> >> Unless there is a way to get a perf file with only the AUXTRACE event and no others? I think that one
> >> might have no timestamp set. Otherwise other events will always have timestamps so spe->timeless_decoding
> >> is always false.
> > 
> > Good point.  To be honest, I never noticed this issue until you
> > mentioned this.
> > 
> > We should fix for the "timeless" flow; and it's questionable for the
> > function arm_spe_recording_options(), except for setting
> > PERF_SAMPLE_TIME, it also hard codes for setting
> > PERF_SAMPLE_CPU and PERF_SAMPLE_TID.  Might need to carefully go
> > through this function.
> > 
> 
> Yeah, it's not strictly related to your change, which is definitely an improvement.
> But maybe we should have a look at the SPE implementation relating to timestamps as a whole.

Just now I sent another patch series "perf arm-spe: Correct recording
configurations", which is the following up for the issue you found at
here.

After correcting sample flags, and combining with current patch series
"perf arm-spe: Enable timestamp", I verified the Arm SPE decoding
flows for "timeless" decoding, which can work as expected.

So I think we can move forward for this patch series, for easier review,
I have uploaded my testing branch wiht the complete patches [1].  Could
you help confirm if this works for you?  Thanks!

Leo

[1] https://github.com/Leo-Yan/linux/tree/perf_arm_spe_timestamp_v4_with_correcting_sample_flags