linux-kernel - Re: [PATCH RFC 2/9] perf metrics: Don't iter sys metrics if we already found a CPU match

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Date:   Tue, 11 Jul 2023 22:40:08 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     John Garry <john.g.garry@...cle.com>
Cc:     acme@...nel.org, namhyung@...nel.org, jolsa@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        renyu.zj@...ux.alibaba.com, shangxiaojing@...wei.com,
        zhangshaokun@...ilicon.com, qiangqing.zhang@....com,
        kjain@...ux.ibm.com, kan.liang@...ux.intel.com
Subject: Re: [PATCH RFC 2/9] perf metrics: Don't iter sys metrics if we
 already found a CPU match

On Mon, Jul 3, 2023 at 6:09 AM John Garry <john.g.garry@...cle.com> wrote:
>
> On 30/06/2023 18:41, Ian Rogers wrote:
> > On Wed, Jun 28, 2023 at 3:30 AM John Garry<john.g.garry@...cle.com>  wrote:
> >> In metricgroup__add_metric() we still iter the sys metrics if we already
> >> found a match from the CPU table, which is pretty pointless, so don't
> >> bother.
> >>
> >> Signed-off-by: John Garry<john.g.garry@...cle.com>
> >> ---
> >>   tools/perf/util/metricgroup.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> >> index 4389ccd29fe7..8d2ac2513530 100644
> >> --- a/tools/perf/util/metricgroup.c
> >> +++ b/tools/perf/util/metricgroup.c
> >> @@ -1261,6 +1261,12 @@ static int metricgroup__add_metric(const char *pmu, const char *metric_name, con
> >>
> >>                  has_match = data.has_match;
> >>          }
>
> Hi Ian,
>
> >> +
> >> +       if (has_match) {
> >> +               ret = 0;
> >> +               goto out;
> >> +       }
> >> +
> > I think this can just be:
> >
> > if (!has_match)
>
> But ret has no initial value
>
> >
> > However, I'm not sure I agree with the intent of the change. We may
> > have a metric like IPC and want it to apply to all types of CPU, GPU,
> > etc. If we short-cut here then that won't be possible.
>
> A few points to make on this:
> - Currently we don't have any same-named metrics like this, so not much
> use in supporting it in the code (yet).

We have same named metrics for heterogeneous CPU PMUs:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/pmu-events/arch/x86/alderlake/adl-metrics.json?h=perf-tools-next#n304
cpu_atom
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/pmu-events/arch/x86/alderlake/adl-metrics.json?h=perf-tools-next#n1125
cpu_core

> - Even if we had some same-named metrics, I am not sure if it even works
> properly. Do we have any uncore PMU metrics which have same name as CPU
> metrics?

So I was thinking IPC was a generic concept that would apply to a
co-processor on a network card, a GPU, etc.

> - Further to the previous point, do we really want same-named metrics
> for different PMUs in the future? I think event / metric names need to
> be chosen carefully to avoid clash for other PMUs or keywords. For your
> example, if I did ask for IPC metric, I'd like to be able to just know
> I'm getting IPC metric for CPUs or some other PMUs, but not both.

At the moment if you request an event without a PMU, say instructions
retired, we will attempt to open the event on every PMU - legacy
events (PERF_TYPE_HARDWARE, PERF_TYPE_HW_CACHE) only try the core
PMUs. It would seem consistent if metrics tried to open on every PMU
like most events.

Thanks,
Ian

> Thanks,
> John
>
> >