2023-01-12 03:47:40

by Yang Jihong

Subject: [PATCH] perf/core: Fix account interrupt throttle

In literal sense of "max_samples_per_tick", if hwc->interrupts ==
max_samples_per_tick, it should not be throttled, therefore, the judgment
condition should be changed to "hwc->interrupts > max_samples_per_tick".

In fact, this may cause the hardlockup to fail, The minimum value of
max_samples_per_tick may be 1, in this case, the return value of
__perf_event_account_interrupt function is 1.
As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
architecture as an example, see x86_pmu_handle_irq).

Signed-off-by: Yang Jihong <[email protected]>
---
kernel/events/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d56328e5080e..ced98e028d86 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9414,7 +9414,7 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
} else {
hwc->interrupts++;
if (unlikely(throttle
- && hwc->interrupts >= max_samples_per_tick)) {
+ && hwc->interrupts > max_samples_per_tick)) {
__this_cpu_inc(perf_throttled_count);
tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
hwc->interrupts = MAX_INTERRUPTS;
--
2.30.GIT

2023-01-28 01:28:41

by Yang Jihong

Subject: Re: [PATCH] perf/core: Fix account interrupt throttle

Hello,

PING

Thanks,
Yang

On 2023/1/12 11:38, Yang Jihong wrote:
> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
> max_samples_per_tick, it should not be throttled, therefore, the judgment
> condition should be changed to "hwc->interrupts > max_samples_per_tick".
>
> In fact, this may cause the hardlockup to fail, The minimum value of
> max_samples_per_tick may be 1, in this case, the return value of
> __perf_event_account_interrupt function is 1.
> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
> architecture as an example, see x86_pmu_handle_irq).
>
> Signed-off-by: Yang Jihong <[email protected]>
> ---
> kernel/events/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d56328e5080e..ced98e028d86 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9414,7 +9414,7 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
> } else {
> hwc->interrupts++;
> if (unlikely(throttle
> - && hwc->interrupts >= max_samples_per_tick)) {
> + && hwc->interrupts > max_samples_per_tick)) {
> __this_cpu_inc(perf_throttled_count);
> tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
> hwc->interrupts = MAX_INTERRUPTS;
>

2023-02-06 01:28:46

by Yang Jihong

Subject: Re: [PATCH] perf/core: Fix account interrupt throttle

Hello,

Ping again, please take time to review, thanks.


Thanks,
Yang

On 2023/1/28 9:28, Yang Jihong wrote:
> Hello,
>
> PING
>
> Thanks,
> Yang
>
> On 2023/1/12 11:38, Yang Jihong wrote:
>> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
>> max_samples_per_tick, it should not be throttled, therefore, the judgment
>> condition should be changed to "hwc->interrupts > max_samples_per_tick".
>>
>> In fact, this may cause the hardlockup to fail, The minimum value of
>> max_samples_per_tick may be 1, in this case, the return value of
>> __perf_event_account_interrupt function is 1.
>> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
>> architecture as an example, see x86_pmu_handle_irq).
>>
>> Signed-off-by: Yang Jihong <[email protected]>
>> ---
>>   kernel/events/core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index d56328e5080e..ced98e028d86 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -9414,7 +9414,7 @@ __perf_event_account_interrupt(struct perf_event
>> *event, int throttle)
>>       } else {
>>           hwc->interrupts++;
>>           if (unlikely(throttle
>> -                 && hwc->interrupts >= max_samples_per_tick)) {
>> +                 && hwc->interrupts > max_samples_per_tick)) {
>>               __this_cpu_inc(perf_throttled_count);
>>               tick_dep_set_cpu(smp_processor_id(),
>> TICK_DEP_BIT_PERF_EVENTS);
>>               hwc->interrupts = MAX_INTERRUPTS;
>>
>
> .