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Date:   Wed, 23 Mar 2022 23:54:44 +0800
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Subject: Re: [External] Re: [PATCH v2] psi: report zeroes for CPU full at the
 system level
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To:     peterz@infradead.org
Cc:     Johannes Weiner <hannes@cmpxchg.org>, corbet@lwn.net,
        mingo@redhat.com, surenb@google.com, ebiggers@google.com,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        songmuchun@bytedance.com,
        Martin Steigerwald <Martin.Steigerwald@proact.de>
References: <20220309111445.86484-1-zhouchengming@bytedance.com>
 <Yij8m9qHtvNKyGMK@cmpxchg.org>
From:   Chengming Zhou <zhouchengming@bytedance.com>
In-Reply-To: <Yij8m9qHtvNKyGMK@cmpxchg.org>
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On 2022/3/10 3:14 上午, Johannes Weiner wrote:
> On Wed, Mar 09, 2022 at 07:14:45PM +0800, Chengming Zhou wrote:
>> Martin find it confusing when look at the /proc/pressure/cpu output,
>> and found no hint about that CPU "full" line in psi Documentation.
>>
>> % cat /proc/pressure/cpu
>> some avg10=0.92 avg60=0.91 avg300=0.73 total=933490489
>> full avg10=0.22 avg60=0.23 avg300=0.16 total=358783277
>>
>> The PSI_CPU_FULL state is introduced by commit e7fcd7622823
>> ("psi: Add PSI_CPU_FULL state"), which mainly for cgroup level,
>> but also counted at the system level as a side effect.
>>
>> Naturally, the FULL state doesn't exist for the CPU resource at
>> the system level. These "full" numbers can come from CPU idle
>> schedule latency. For example, t1 is the time when task wakeup
>> on an idle CPU, t2 is the time when CPU pick and switch to it.
>> The delta of (t2 - t1) will be in CPU_FULL state.
>>
>> Another case all processes can be stalled is when all cgroups
>> have been throttled at the same time, which unlikely to happen.
>>
>> Anyway, CPU_FULL metric is meaningless and confusing at the
>> system level. So this patch will report zeroes for CPU full
>> at the system level, and update psi Documentation accordingly.
>>
>> Fixes: e7fcd7622823 ("psi: Add PSI_CPU_FULL state")
>> Reported-by: Martin Steigerwald <Martin.Steigerwald@proact.de>
>> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> 
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> Peter, would you mind picking this up for 5.18?

Hi Peter, ping...

Maybe the subject should start with "sched/psi", to be easier to notice ;-)

Thanks.

> 
> Thanks!