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Subject: Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by
 perf throttle
From:   Yang Jihong <yangjihong1@huawei.com>
To:     <peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>,
        <mark.rutland@arm.com>, <alexander.shishkin@linux.intel.com>,
        <jolsa@kernel.org>, <namhyung@kernel.org>, <irogers@google.com>,
        <eranian@google.com>, <linux-perf-users@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20230227023508.102230-1-yangjihong1@huawei.com>
 <12782722-103e-88a9-df3e-6815b4734bc3@huawei.com>
Message-ID: <37d019af-191c-9955-2417-b7cfa5e5efa3@huawei.com>
Date:   Wed, 22 Mar 2023 15:36:22 +0800
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Hello,

PING.

This patch has not been responded.
Please take time to check whether the fix solution is OK.
Look forward to reviewing the patch. Thanks :)

Thanks,
Yang.

On 2023/3/6 9:14, Yang Jihong wrote:
> Hello,
> 
> PING.
> 
> Thanks,
> Yang.
> 
> On 2023/2/27 10:35, Yang Jihong wrote:
>> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
>> introduces a change in throttling threshold judgment. Before this,
>> compare hwc->interrupts and max_samples_per_tick, then increase
>> hwc->interrupts by 1, but this commit reverses order of these two
>> behaviors, causing the semantics of max_samples_per_tick to change.
>> 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).
>>
>> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>
>> Changes since v2:
>>    - Add fixed commit.
>>
>> Changes since v1:
>>    - Modify commit title.
>>
>>   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 f79fd8b87f75..0540a8653906 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -9434,7 +9434,7 @@ __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;
>>
> 
> .