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

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Message-ID: <20210416132104.GG1011890@leoy-ThinkPad-X240s>
Date:   Fri, 16 Apr 2021 21:21:04 +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

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

[...]

> >> 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.

Totally agree, at least this patch series should not introduce any
barrier for timeless case.  I will go back to verify it; if you'd
like to fix timeless issue, please feel free to go ahead.

Thanks,
Leo