Re: [RFC PATCH v2 0/5] topdown with metrics

[Andrew Kilroy]

On 20/01/2022 09:26, John Garry wrote:
> On 11/01/2022 15:07, Andrew Kilroy wrote:
> > This patch series adds the ability for the --topdown option to use
> > metrics (defined in json files in the pmu-events directory) to describe
> > how to calculate and determine the output columns for topdown level 1.
> >
> > For this to work, a number of metrics have to be defined for the
> > relevant processor with the MetricGroup name "TopDownL1".  perf will
> > arrange for the events defined in each metric to be collected, and each
> > metric will be displayed in the output, as if
> >
> >    perf stat -M 'TopDownL1' --metric-only -- exampleapp
> >
> > had been used.
> >
> > Topdown was already implemented where certain kernel events are defined.
> > If these kernel events are defined, the new json metrics behaviour is
> > not used.  The json metrics approach is only used if the kernel events
> > are absent.
> >
> > The last patch in the series disables the json metrics behaviour on x86.
> > This is because of concerns that due to SMT it's not straightforward to
> > express the various formulas as json for certain x86 cpus.  See
>
> I suppose this solution is ok.

Thanks, would you mind giving it a Reviewed-By?

> A concern is that today we only have 1x arm64 platform which actually 
> supports this in mainline.
>
> Do you have any more which you plan to support?

The Neoverse cores, mainly.

> I think that it's the frontend bound and fetch_bubble event which 
> doesn't have a standard arm solution.
>
> Note that I do have a series for perf tool which can read arm cpu pmu 
> sysfs events folder to find events which are implemented (I don't think 
> all required events are mandated) and match that against the common arch 
> events JSON, so that we don't need a JSON definition file for each core 
> implementation from all implementators - this would improve scalability. 
> However a concern is that some events - like inst_spec - have imp def 
> meaning, so may not be good to always use by default for all cores metrics.
>
> Thanks,
> John

Thanks,
Andrew