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

[Arnaldo Carvalho de Melo]

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@xxxxxxxxxxxxxxx> 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