Re: [PATCH 1/3] perf bench futex: benchmark only online CPUs

[Davidlohr Bueso]

On Thu, 23 Nov 2017, Arnaldo Carvalho de Melo wrote:

> Em Thu, Nov 23, 2017 at 12:09:48PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Wed, Nov 22, 2017 at 06:25:28PM -0600, Kim Phillips escreveu:
> > > From: James Yang <james.yang@xxxxxxx>
> > >
> > > The "perf bench futex" benchmarks have a problem when not all CPUs in
> > > the system are online:  perf assumes the CPUs that are online are
> > > contiguously numbered and assigns processor affinity to the threads by
> > > modulo striping.  When the online CPUs are not contiguously numbered,
> > > perf errors out with:

Good catch. Non contiguously numbered cpus was certainly not something I had
considered.

> > >
> > > $ echo 0 | sudo tee /sys/devices/system/cpu/cpu3/online
> > > 0
> > > $ ./oldperf bench futex all
> > > perf: pthread_create: Operation not permitted
> > > Run summary [PID 14934]: 7 threads, each operating on 1024 [private] futexes for 10 secs.
> > >
> > > $
> > >
> > > This patch makes perf not assume all CPUs configured are online, and
> > > adds a mapping table to stripe affinity across the CPUs that are
> > > online.
> >
> > So, have you looked at tools/perf/util/cpumap.c? I think you can use:
> >
> > 	int i;
> > 	struct cpu_map *cpus = cpu_map__new(NULL);
> >
> > 	for (i = 0; i < cpus->nr; ++i) {
> > 		int cpu = cpus->map[i];
> > 		...
> > 	}
> >
> > No?

Ah, I was just thinking there should be something like this in perf already :)

> But then, this can be done later, as probably will result in more
> changes, I'm continuing to review the other patches.

Unsure if you're implying otherwise, but I would strongly prefer a v2 was sent
to use the perf's cpumap.c.

Thanks,
Davidlohr