From: Chengming Zhou <zhouchengming@bytedance.com>
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>
Subject: Re: [External] Re: [PATCH v2] psi: report zeroes for CPU full at the system level
Date: Wed, 23 Mar 2022 23:54:44 +0800 [thread overview]
Message-ID: <b435553f-930e-52fa-86fb-0d1619bb69b3@bytedance.com> (raw)
In-Reply-To: <Yij8m9qHtvNKyGMK@cmpxchg.org>
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!
prev parent reply other threads:[~2022-03-23 15:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-09 11:14 [PATCH v2] psi: report zeroes for CPU full at the system level Chengming Zhou
2022-03-09 19:14 ` Johannes Weiner
2022-03-23 15:54 ` Chengming Zhou [this message]
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