Re: [PATCH v2 2/2] perf/arm-cmn: Allow userspace to select the PMU's CPU

[sashiko-bot@kernel.org]

> arm_cmn_probe() picks the CPU that owns the PMU with
> 
> 	cmn->cpu = cpumask_local_spread(0, dev_to_node(cmn->dev));
> 
> and arm_cmn_event_init() then binds every event to it unconditionally.
> That choice is only revisited by the CPU hotplug callbacks, so in
> practice the PMU stays on the first CPU local to the interconnect's NUMA
> node, which is usually CPU 0.
> 
> All of the PMU's recurring work therefore lands on one CPU. This is
> problematic on systems which reserve particular CPUs for latency
> sensitive work or confine background activity to a chosen set of
> housekeeping CPUs.
> 
> There is no way to set it explicitly. perf_event_open() and 'perf stat
> [ ... ]
> The attribute expresses a preference rather than a guarantee. The
> hotplug callbacks may still move the PMU, for example when the chosen
> CPU is offlined.
> 
> Signed-off-by: Haris Okanovic <harisokn@amazon.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260930231127.3094040-1-harisokn@amazon.com?part=2