Re: [PATCH v6 7/9] fs/resctrl: Do not invoke smp_processor_id() in preemptible context

[Reinette Chatre]

Hi Chenyu,

On 7/25/26 2:23 AM, Chen Yu wrote:
> From: Tony Luck <tony.luck@xxxxxxxxx>
> 
> LLC occupancy can be read on any CPU when the counter is accessed via
> MMIO, so such an event is read from task context on whatever CPU the
> caller happens to be running on rather than being bounced to a CPU in
> the monitoring domain. mon_evt::any_cpu marks these CPU-agnostic events.

Please let the context describe what the *current* code does. This changelog
describes context that does not exist (yet) and then presents the change in
this patch as a bugfix. This is not accurate and misrepresents this change.

> 
> __l3_mon_event_count() calls smp_processor_id() to find the CPU to read
> from. For an any_cpu event that lookup is unsafe:
> the code runs in preemptible task context, so smp_processor_id() emits a
> debug warning.
> 
> Skip the current-CPU lookup when an event's any_cpu flag is set, events with
> this flag do not require execution on a specific CPU. For legacy MSR-based
> access, update rmid_read::err if the reading of the event was dispatched to
> a wrong CPU, according to the change at:
> https://lore.kernel.org/lkml/6b3c66a49788828bd8c04a6911bd74c91ccd56f3.1782857711.git.reinette.chatre@xxxxxxxxx/

This has been merged now so it should not be necessary to call this out,
at least in this format

> 
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> Tested-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
> ---
Reinette