Re: [Patch v2 3/9] perf/x86: Update cap_user_rdpmc base on rdpmc user disable state

[Mi, Dapeng]

On 6/9/2026 10:48 PM, Peter Zijlstra wrote:
> On Tue, Jun 09, 2026 at 01:02:16PM +0800, Dapeng Mi wrote:
>
>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index 3bd0522afe6d..6cd95b8e31cb 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -2797,6 +2797,9 @@ void arch_perf_update_userpage(struct perf_event *event,
>>  	userpg->cap_user_time_zero = 0;
>>  	userpg->cap_user_rdpmc =
>>  		!!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
>> +	if (x86_pmu_has_rdpmc_user_disable(event->pmu) &&
>> +	    event->hw.config & ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE)
>> +		userpg->cap_user_rdpmc = 0;
>>  	userpg->pmc_width = x86_pmu.cntval_bits;
>>  
>>  	if (!using_native_sched_clock() || !sched_clock_stable())
> Remember, this is evaluated very very often. So it makes more sense to
> ensure the hw.flags state is correct such that this remains a simple
> expression.

Yes, directly manipulating PERF_EVENT_FLAG_USER_READ_CNT is a simpler way.
Thanks.

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 6cd95b8e31cb..3bd0522afe6d 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2797,9 +2797,6 @@ void arch_perf_update_userpage(struct perf_event *event,
        userpg->cap_user_time_zero = 0;
        userpg->cap_user_rdpmc =
                !!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
-       if (x86_pmu_has_rdpmc_user_disable(event->pmu) &&
-           event->hw.config & ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE)
-               userpg->cap_user_rdpmc = 0;
        userpg->pmc_width = x86_pmu.cntval_bits;

        if (!using_native_sched_clock() || !sched_clock_stable())
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index efd9caa3502c..afb86e5611bf 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3532,10 +3532,13 @@ static void
intel_pmu_update_rdpmc_user_disable(struct perf_event *event)
         */
        if (x86_pmu.attr_rdpmc == X86_USER_RDPMC_ALWAYS_ENABLE ||
            (x86_pmu.attr_rdpmc == X86_USER_RDPMC_CONDITIONAL_ENABLE &&
-            event->ctx->task))
+            event->ctx->task)) {
                event->hw.config &= ~ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE;
-       else
+       } else {
                event->hw.config |= ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE;
+               if (event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT)
+                       event->hw.flags &= ~PERF_EVENT_FLAG_USER_READ_CNT;
+       }
 }