Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5

[James Clark]

On 15/08/2024 4:53 pm, Arnaldo Carvalho de Melo wrote:
> On Thu, Aug 15, 2024 at 12:27:21PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Thu, Aug 15, 2024 at 04:15:41PM +0100, James Clark wrote:
> > > In one of your investigations here
> > > https://lore.kernel.org/lkml/Zld3dlJHjFMFG02v@x1/ comparing "cycles",
> > > "cpu-cycles" and "cpu_cycles" events on Arm you say only some of them open
> > > events on both core types. I wasn't able to reproduce that on
> > > perf-tools-next (27ac597c0e) or v6.9 (a38297e3fb) for perf record or stat. I
> > > guessed the 6.9 tag because you only mentioned it was on tip and it was 29th
> > > May. For me they all open exactly the same two legacy events with the
> > > extended type ID set.
> > >
> > > It looks like the behavior you see would be caused by either missing this
> > > kernel change:
> > >
> > >    5c81672865 ("arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability")
> > >     (v6.6 release)
>
> What I have now is:
>
> 6.1.92-15907-gf36fd2695db3
>
> It was a bit older, but 6.1 ish as well, I'll try to either get a new
> kernel from Libre Computer or build one myself.
>
> - Arnaldo

Thanks for the confirmation. In that case you may not even need to 
retest. I was only wondering if it was broken from v6.6 onwards, but 6.1 
not working is expected. And I'm certain that you'll find any later 
versions working.

> > > Or this userspace change, but unlikely as it was a fix for Apple M hardware:
> > >
> > >    25412c036 ("perf print-events: make is_event_supported() more robust")
> > >     (v6.9 release)
> > >
> > > Do you remember if you were using a new kernel or only testing a new Perf?
> >
> > I normally use the distro/SoC provided kernel, didn't I add the 'uname
> > -a' output in those investigations (/me slaps himself in the face
> > speculatively...)?