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

Chen, Yu C
2025-10-30T06:14:44Z

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

thanks,
Chenyu