linux-kernel - Re: [RFC 00/10] perf tools: Add support to reuse metric

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Message-ID: <20200627124650.GE29008@kernel.org>
Date:   Sat, 27 Jun 2020 09:46:50 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Michael Petlan <mpetlan@...hat.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        John Garry <john.garry@...wei.com>,
        "Paul A. Clarke" <pc@...ibm.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC 00/10] perf tools: Add support to reuse metric

Em Fri, Jun 26, 2020 at 02:44:14PM -0700, Ian Rogers escreveu:
> On Fri, Jun 26, 2020 at 2:25 PM Andi Kleen <ak@...ux.intel.com> wrote:
> > On Fri, Jun 26, 2020 at 09:47:10PM +0200, Jiri Olsa wrote:
> > > this patchset is adding the support to reused metric in another
> > > metric. The metric needs to be referenced by 'metric:' prefix.

> > Why is the prefix needed?

> > Could just look it up without prefix.

> The name could be a metric or an event, the logic for each is quite
> different. You could look up an event and when it fails assume it was
> a metric, but I like the simplicity of this approach. Maybe this
> change could be adopted more widely with something like "perf stat -e
> metric:IPC -a -I 1000" rather than the current "perf stat -M IPC -a -I
> 1000".

Humm, the more concise, the better, so I think that we should use
metric: when we notice ambiguity, i.e. we should first lookup the
provided name as an event, and even if it resolves, look it up as well
as a metric, if both lookups work, then one need to disambiguate.

But then, why should we pick a name for a metric that is also a name for
an event? Can you think about a concrete case? Can't we detect this at
build time, when introducing the new metric and bail out?

- Arnaldo