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

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Date: Tue, 4 Jun 2024 20:22:26 +0800
From: Yicong Yang <yangyicong@...wei.com>
To: Ian Rogers <irogers@...gle.com>
CC: <yangyicong@...ilicon.com>, <will@...nel.org>, <mark.rutland@....com>,
	<acme@...nel.org>, <namhyung@...nel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-perf-users@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <peterz@...radead.org>, <mingo@...hat.com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<james.clark@....com>, <dongli.zhang@...cle.com>,
	<jonathan.cameron@...wei.com>, <prime.zeng@...ilicon.com>,
	<linuxarm@...wei.com>
Subject: Re: [PATCH 2/3] perf: arm_pmu: Only show online CPUs in device's
 "cpus" attribute

On 2024/6/4 0:20, Ian Rogers wrote:
> On Mon, Jun 3, 2024 at 2:33 AM Yicong Yang <yangyicong@...wei.com> wrote:
>>
>> From: Yicong Yang <yangyicong@...ilicon.com>
>>
>> When there're CPUs offline after system booting, perf will failed:
>> [root@...alhost ~]# /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.