Re: [PATCH v4 08/10] drivers/perf: hisi: Export associated CPUs of each PMU through sysfs

[Will Deacon <will@kernel.org>]

On Tue, Dec 03, 2024 at 08:50:47PM +0800, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@hisilicon.com>
> 
> Although the event of the uncore PMU can only be opened on a single
> CPU, some PMU does have the affinity on a range of CPUs. For example
> the L3C PMU is associated to the CPUs sharing the L3T it monitors.
> Users may infer this affinity by the PMU name which may have SCCL ID
> and CCL ID encoded (for L3C etc), but it's not that straightforward.
> So export this information by adding an "associated_cpus" sysfs
> attribute then user can get this directly.
> 
> Reviewed-by: Jonathan Cameron <Joanthan.Cameron@huawei.com>
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> ---
>  Documentation/admin-guide/perf/hisi-pmu.rst |  5 ++++-
>  drivers/perf/hisilicon/hisi_uncore_pmu.c    | 10 ++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/perf/hisi-pmu.rst b/Documentation/admin-guide/perf/hisi-pmu.rst
> index 5cc248d18c63..48992a0b8e94 100644
> --- a/Documentation/admin-guide/perf/hisi-pmu.rst
> +++ b/Documentation/admin-guide/perf/hisi-pmu.rst
> @@ -35,7 +35,10 @@ e.g. hisi_sccl1_hha0/rx_operations is RX_OPERATIONS event of HHA index #0 in
>  SCCL ID #1.
>  
>  The driver also provides a "cpumask" sysfs attribute, which shows the CPU core
> -ID used to count the uncore PMU event.
> +ID used to count the uncore PMU event. An "associated_cpus" sysfs attribute is
> +also provided to show the CPUs associated with this PMU. The "cpumask" indicates
> +the CPUs to open the events, usually as a hint for userspaces tools like perf.
> +It only contains one associated CPU from the "associated_cpus".

What is userspace expected to do with this information? Can you point me
to patches that add the corresponding support to the 'perf' tool, please?

Will