Re: [PATCH v13 11/32] x86,fs/resctrl: Handle events that can be read from any CPU

Chen, Yu C
2025-10-30T16:18:30Z

On 10/30/2025 11:54 PM, Luck, Tony wrote:
> On Thu, Oct 30, 2025 at 02:14:27PM +0800, Chen, Yu C wrote:
>> Hi Tony,
>>
>> On 10/30/2025 12:20 AM, Tony Luck wrote:
>>> resctrl assumes that monitor events can only be read from a CPU in the
>>> cpumask_t set of each domain. This is true for x86 events accessed
>>> with an MSR interface, but may not be true for other access methods such
>>> as MMIO.
>>>
>>> Introduce and use flag mon_evt::any_cpu, settable by architecture, that
>>> indicates there are no restrictions on which CPU can read that event.
>>>
>>> Signed-off-by: Tony Luck <tony.luck@intel.com>
>>
>> [snip]
>>
>>> -void resctrl_enable_mon_event(enum resctrl_event_id eventid)
>>> +void resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu)
>>> {
>>> if (WARN_ON_ONCE(eventid < QOS_FIRST_EVENT || eventid >= QOS_NUM_EVENTS))
>>> return;
>>> @@ -984,6 +984,7 @@ void resctrl_enable_mon_event(enum resctrl_event_id eventid)
>>> return;
>>> }
>>> + mon_event_all[eventid].any_cpu = any_cpu;
>>> mon_event_all[eventid].enabled = true;
>>> }
>>
>> It seems that cpu_on_correct_domain() was dropped, due to
>> the refactor of __mon_event_count() in patch 0006 means it is no
>> longer needed. But we still invoke smp_processor_id() in preemptible
>> context in __l3_mon_event_count() before further checkings, which would
>> cause a warning.
>> [ 4266.361951] BUG: using smp_processor_id() in preemptible [00000000] code:
>> grep/1603
>> [ 4266.363231] caller is __l3_mon_event_count+0x30/0x2a0
>> [ 4266.364250] Call Trace:
>> [ 4266.364262] <TASK>
>> [ 4266.364273] dump_stack_lvl+0x53/0x70
>> [ 4266.364289] check_preemption_disabled+0xca/0xe0
>> [ 4266.364303] __l3_mon_event_count+0x30/0x2a0
>> [ 4266.364320] mon_event_count+0x22/0x90
>> [ 4266.364334] rdtgroup_mondata_show+0x108/0x390
>> [ 4266.364353] seq_read_iter+0x10d/0x450
>> [ 4266.364368] vfs_read+0x215/0x330
>> [ 4266.364386] ksys_read+0x6b/0xe0
>> [ 4266.364401] do_syscall_64+0x57/0xd70
>
> I didn't notice this in my testing. Is this in your region aware
> tree? If you are still using RDT_RESOURCE_L3 then I can see how
> you got this call trace.
>

Yes, it was tested on the region aware tree.

> Maybe you need to dig cpu_on_correct_domain() back up and apply
> it to __l3_mon_event_count()?
>

Got it, will do.

Thanks,
Chenyu