linux-kernel - Re: [PATCH v1 4/7] perf cs-etm: Add PID format into metadata

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Date:   Mon, 11 Jan 2021 21:12:05 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Kiss <Daniel.Kiss@....com>,
        Denis Nikitin <denik@...omium.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/7] perf cs-etm: Add PID format into metadata

On Mon, Jan 11, 2021 at 09:45:12AM +0000, Suzuki Kuruppassery Poulose wrote:
> Hi Leo,
> 
> On 1/9/21 7:44 AM, Leo Yan wrote:
> > It's possible for CoreSight to trace PID in either CONTEXTIDR_EL1 or
> > CONTEXTIDR_EL2, the PID format info is used to distinguish the PID
> > is traced in which register.
> > 
> > This patch saves PID format into the metadata when record.
> 
> The patch looks good to me. One minor suggestion below
> 
> > 
> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > ---
> >   tools/perf/arch/arm/util/cs-etm.c | 21 +++++++++++++++++++++
> >   tools/perf/util/cs-etm.c          |  2 ++
> >   tools/perf/util/cs-etm.h          |  2 ++
> >   3 files changed, 25 insertions(+)
> > 
> > diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> > index fad7b6e13ccc..ee78df3b1b07 100644
> > --- a/tools/perf/arch/arm/util/cs-etm.c
> > +++ b/tools/perf/arch/arm/util/cs-etm.c
> > @@ -613,6 +613,7 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
> >   	struct cs_etm_recording *ptr =
> >   			container_of(itr, struct cs_etm_recording, itr);
> >   	struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu;
> > +	u64 pid_fmt;
> >   	/* first see what kind of tracer this cpu is affined to */
> >   	if (cs_etm_is_etmv4(itr, cpu)) {
> > @@ -641,6 +642,16 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
> >   				      metadata_etmv4_ro
> >   				      [CS_ETMV4_TRCAUTHSTATUS]);
> > +		/*
> > +		 * The PID format will be used when decode the trace data;
> > +		 * based on it the decoder will make decision for setting
> > +		 * sample's PID as context_id or VMID.
> > +		 */
> > +		pid_fmt = perf_pmu__format_bits(&cs_etm_pmu->format, "pid");
> > +		if (!pid_fmt)
> > +			pid_fmt = 1ULL << ETM_OPT_CTXTID;
> > +		info->priv[*offset + CS_ETMV4_PID_FMT] = pid_fmt;
> > +
> 
> Given we do this same step twice here in this function and also in patch 2.
> I am wondering if this could be made into a small helper function ?
> 
> static u64 cs_etm_pmu_format_pid(cs_etm_pm)
> {
> 	pid_fmt = perf_pmu__format_bits(&cs_etm_pmu->format, "pid");
> 	/*
> 	 * An older kernel doesn't expose this, so fall back to using
> 	 * CTXTID.
> 	 */
> 	if (!pid_fmt)
> 		pid_fmt = 1ULL << ETM_OPT_CTXTID;
> 	return pid_fmt;
> }

Agreed; will follow up this suggestion.

Thanks,
Leo