Re: [PATCHv4 00/19] perf metric: Add support to reuse metric

[Paul A. Clarke]

On Wed, Jul 29, 2020 at 11:18:49AM +0200, Jiri Olsa wrote:
> this patchset is adding the support to reused metric in
> another metric.
> 
> For example, to define IPC by using CPI with change like:
> 
>      {
>          "BriefDescription": "Instructions Per Cycle (per Logical Processor)",
> -        "MetricExpr": "INST_RETIRED.ANY / CPU_CLK_UNHALTED.THREAD",
> +        "MetricExpr": "1/CPI",
>          "MetricGroup": "TopDownL1",
>          "MetricName": "IPC"
>      },
> 
> I won't be able to find all the possible places we could
> use this at, so I wonder you guys (who was asking for this)
> would try it and come up with comments if there's something
> missing or we could already use it at some places.
> 
> It's based on Arnaldo's tmp.perf/core.
> 
> v4 changes:
>   - removed acks from patch because it changed a bit
>     with the last fixes:
>       perf metric: Collect referenced metrics in struct metric_ref_node
>   - fixed runtime metrics [Kajol Jain]
>   - increased recursion depth [Paul A. Clarke]
>   - changed patches due to dependencies:
>       perf metric: Collect referenced metrics in struct metric_ref_node
>       perf metric: Add recursion check when processing nested metrics
>       perf metric: Rename struct egroup to metric
>       perf metric: Rename group_list to metric_list
> 
> Also available in here:
>   git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   perf/metric

I built and ran from the above git branch, and things seem to work.
Indeed, I was able to apply my changes to exploit the new capabilities
via modifications to tools/perf/pmu-events/arch/powerpc/power9/metrics.json,
as I posted earlier (and will submit once this set gets merged).

Tested-by: Paul A. Clarke <pc@xxxxxxxxxx>

One thing I noted, but which also occurs without these patches, is that
the perf metrics are not computed unless run as root:
--
$ perf stat --metrics br_misprediction_percent command

 Performance counter stats for 'command':

     1,823,530,051      pm_br_pred:u                                                
         2,662,705      pm_br_mpred_cmpl:u                                          

$ /usr/bin/sudo perf stat --metrics br_misprediction_percent command

 Performance counter stats for 'command':

     1,824,655,269      pm_br_pred                #     0.09 br_misprediction_percent
         1,654,466      pm_br_mpred_cmpl
--

Is that expected?  I don't think it's always been that way.

PC