[PATCH] perf print-events: make is_event_supported() more robust

[Mark Rutland]

On Wed, Jan 17, 2024 at 09:05:25AM +0000, Marc Zyngier wrote:
> Hi Mark,
> 
> On Tue, 16 Jan 2024 17:03:48 +0000,
> Mark Rutland <mark.rutland at arm.com> wrote:
> > 
> > Currently the perf tool doesn't deteect support for extneded event types
> > on Apple M1/M2 systems, and will not auto-expand plain PERF_EVENT_TYPE
> > hardware events into per-PMU events. This is due to the detection of
> > extended event types not handling mandatory filters required by the
> > M1/M2 PMU driver.
> 
> Thanks for looking into this.
> 
> I've given your patch a go on my M1 box, and it indeed makes things
> substantially better:
> 
> $ sudo ./perf stat -e cycles ~/hackbench 100 process 1000
> Running with 100*40 (== 4000) tasks.
> Time: 3.419
> 
>  Performance counter stats for '/home/maz/hackbench 100 process 1000':
> 
>    174,783,472,090      apple_firestorm_pmu/cycles/                                             (93.10%)
>     39,134,744,813      apple_icestorm_pmu/cycles/                                              (71.86%)
> 
>        3.568145595 seconds time elapsed
> 
>       12.203084000 seconds user
>       55.135271000 seconds sys

Thanks for giving that a spin!

> However, I'm seeing some slightly odd behaviours:
> 
> $ sudo ./perf stat -e cycles:k ~/hackbench 100 process 1000
> Running with 100*40 (== 4000) tasks.
> Time: 3.313
> 
>  Performance counter stats for '/home/maz/hackbench 100 process 1000':
> 
>    <not supported>      apple_firestorm_pmu/cycles:k/                                         
>    <not supported>      apple_icestorm_pmu/cycles:k/                                          
> 
>        3.467568841 seconds time elapsed
> 
>       13.080111000 seconds user
>       53.162099000 seconds sys
> 
> I would have expected it to count, but it didn't. For that to work, I
> have to add the 'H' modifier:

Ok, so that'll have something to do with the way the tool chooses which
perf_evant_attr::exclude_* bits to set. I thought that was the same for plain
events and pmu_name/event/ events, but I could be mistaken.

Is that something you had tried prior to this patch, and did that "just work"
with the explicit pmu_name/event/ syntax prior to this patch?

e.g. did something like:

	perf stat -e apple_firestorm_pmu/cycles/k -e apple_icestorm_pmu/cycles/k ./workload

... happen to work withiout requiring the addition of 'H'?

If so, does that behave the same before/after this patch?

... and could you run that with '-vvv' and dump the output for comparison?

Thanks,
Mark.