Re: [PATCH 2/3] perf: arm_pmu: Only show online CPUs in device's "cpus" attribute

[Yicong Yang]

On 2024/6/4 0:20, Ian Rogers wrote:
> On Mon, Jun 3, 2024 at 2:33 AM Yicong Yang <yangyicong@xxxxxxxxxx> wrote:
>>
>> From: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
>>
>> When there're CPUs offline after system booting, perf will failed:
>> [root@localhost ~]# /home/yang/perf stat -a -e armv8_pmuv3_0/cycles/
>> Error:
>> The sys_perf_event_open() syscall returned with 19 (No such device) for event (cpu-clock).
>> /bin/dmesg | grep -i perf may provide additional information.
> 
> Thanks for debugging this Yicong! The fact cycles is falling back on
> cpu-clock I'm confused by, on ARM the PMU type generally isn't
> PERF_TYPE_HARDWARE and so this fallback shouldn't happen:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/evsel.c?h=perf-tools-next#n2900

It should be brought by config_term_pmu() in [1]. If it's a hardware event term
and not found in the PMU's sysfs, we'll make attr->type to PERF_TYPE_HARDWARE.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/parse-events.c?h=perf-tools-next#n1052

Thanks.