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

Davidlohr Bueso
2017-11-24T15:36:04Z

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@arm.com>
>> >
>> > 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