Subject: Re: [PATCH v2 02/17] perf tools: Configure timestsamp generation in CPU-wide mode

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Fri, 7 Jun 2019 15:34:34 -0300

Em Fri, Jun 07, 2019 at 11:46:32AM -0600, Mathieu Poirier escreveu:
> On Fri, 7 Jun 2019 at 03:41, Suzuki K Poulose <[email-masked]> wrote:
> >
> >
> >
> > On 24/05/2019 18:34, Mathieu Poirier wrote:
> > > When operating in CPU-wide mode tracers need to generate timestamps in
> > > order to correlate the code being traced on one CPU with what is executed
> > > on other CPUs.
> > >
> > > Signed-off-by: Mathieu Poirier <[email-masked]>
> > > ---
> > >   tools/perf/arch/arm/util/cs-etm.c | 57 +++++++++++++++++++++++++++++++
> > >   1 file changed, 57 insertions(+)
> > >
> > > diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> > > index 3912f0bf04ed..be1e4f20affa 100644
> > > --- a/tools/perf/arch/arm/util/cs-etm.c
> > > +++ b/tools/perf/arch/arm/util/cs-etm.c
> > > @@ -99,6 +99,54 @@ static int cs_etm_set_context_id(struct auxtrace_record *itr,
> > >       return err;
> > >   }
> > >
> > > +static int cs_etm_set_timestamp(struct auxtrace_record *itr,
> > > +                             struct perf_evsel *evsel, int cpu)
> > > +{
> > > +     struct cs_etm_recording *ptr;
> > > +     struct perf_pmu *cs_etm_pmu;
> > > +     char path[PATH_MAX];
> > > +     int err = -EINVAL;
> > > +     u32 val;
> > > +
> > > +     ptr = container_of(itr, struct cs_etm_recording, itr);
> > > +     cs_etm_pmu = ptr->cs_etm_pmu;
> > > +
> > > +     if (!cs_etm_is_etmv4(itr, cpu))
> > > +             goto out;
> > > +
> > > +     /* Get a handle on TRCIRD0 */
> > > +     snprintf(path, PATH_MAX, "cpu%d/%s",
> > > +              cpu, metadata_etmv4_ro[CS_ETMV4_TRCIDR0]);
> > > +     err = perf_pmu__scan_file(cs_etm_pmu, path, "%x", &val);
> > > +
> > > +     /* There was a problem reading the file, bailing out */
> > > +     if (err != 1) {
> > > +             pr_err("%s: can't read file %s\n",
> > > +                    CORESIGHT_ETM_PMU_NAME, path);
> > > +             goto out;
> > > +     }
> > > +
> > > +     /*
> > > +      * TRCIDR0.TSSIZE, bit [28-24], indicates whether global timestamping
> > > +      * is supported:
> > > +      *  0b00000 Global timestamping is not implemented
> > > +      *  0b00110 Implementation supports a maximum timestamp of 48bits.
> > > +      *  0b01000 Implementation supports a maximum timestamp of 64bits.
> > > +      */
> > > +     val &= GENMASK(28, 24);
> > > +     if (!val) {
> > > +             err = -EINVAL;
> > > +             goto out;
> > > +     }
> > > +
> > > +     /* All good, let the kernel know */
> > > +     evsel->attr.config |= (1 << ETM_OPT_TS);
> > > +     err = 0;
> > > +
> > > +out:
> > > +     return err;
> > > +}
> > > +
> > >   static int cs_etm_set_option(struct auxtrace_record *itr,
> > >                            struct perf_evsel *evsel, u32 option)
> > >   {
> > > @@ -118,6 +166,11 @@ static int cs_etm_set_option(struct auxtrace_record *itr,
> > >                       if (err)
> > >                               goto out;
> > >                       break;
> > > +             case ETM_OPT_TS:
> > > +                     err = cs_etm_set_timestamp(itr, evsel, i);
> > > +                     if (err)
> > > +                             goto out;
> > > +                     break;
> > >               default:
> > >                       goto out;
> > >               }
> > > @@ -343,6 +396,10 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
> > >               err = cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_CTXTID);
> > >               if (err)
> > >                       goto out;
> > > +
> > > +             err = cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_TS);
> > > +             if (err)
> > > +                     goto out;
> >
> > nit: Could we not do this in one shot, say :
> >
> >         cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_TS | ETM_OPT_CTXTID) ?
> >
> > rather than iterating over the per-CPU events twice ? The cs_etm_set_option()
> > could simply replace the switch() to :
> >
> >         if (option & ETM_OPT_1)
> >                 do_something_for_1()
> >         if (option & ETM_OPT_2)
> >                 do_something_for_2();
> >         if (option & ~(ETM_OPT_1 | ETM_OPT_2 |...))
> >                 /* do unsupported option */
> >
> 
> Yes, that is a good optimization.
> 
> Arnaldo, do you prefer a new set or another patch on top of this one?

On top of it, as this isn't a fix just an optimization, so no need to go
back and fix history to avoid bisection, etc.

Put it in your next set, no need to hurry.

- Arnaldo
 
> Thanks,
> Mathieu
> > Cheers
> > Suzuki

-- 

- Arnaldo

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