linux-kernel - Re: [PATCH 9/9] sched/psi: add PSI_IRQ to track IRQ/SOFTIRQ pressure

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Date:   Fri, 22 Jul 2022 15:14:00 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Chengming Zhou <zhouchengming@...edance.com>, hannes@...xchg.org,
        surenb@...gle.com, mingo@...hat.com, peterz@...radead.org,
        tj@...nel.org, corbet@....net, akpm@...ux-foundation.org,
        rdunlap@...radead.org
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com, cgroups@...r.kernel.org
Subject: Re: [PATCH 9/9] sched/psi: add PSI_IRQ to track IRQ/SOFTIRQ pressure

On 7/22/22 2:13 PM, Chengming Zhou Wrote:
> On 2022/7/22 11:30, Abel Wu wrote:
>> Hi Chengming,
>>
>> On 7/21/22 12:04 PM, Chengming Zhou Wrote:
>>> Now PSI already tracked workload pressure stall information for
>>> CPU, memory and IO. Apart from these, IRQ/SOFTIRQ could have
>>> obvious impact on some workload productivity, such as web service
>>> workload.
>>>
>>> When CONFIG_IRQ_TIME_ACCOUNTING, we can get IRQ/SOFTIRQ delta time
>>> from update_rq_clock_task(), in which we can record that delta
>>> to CPU curr task's cgroups as PSI_IRQ_FULL status.
>>
>> The {soft,}irq affection should be equal to all the runnable tasks
>> on that cpu, not only rq->curr. Further I think irqstall is per-cpu
>> rather than per-cgroup.
> 
> Although IRQ/SOFTIRQ is per-cpu, it's the rq->curr who own the CPU at the time
> and pay for it, meanwhile other groups would be thought as PSI_CPU_FULL.

I don't think rq->curr pays for it if you mean consuming quota here.
And it doesn't seem appropriate to let other groups treat it as cpu
stall because the rq->curr is also the victim rather than the one
causes stall (so it's different from rq->curr causing memstall and
observed as cpustall by others).

> 
> So I think it's reasonable to account this IRQ/SOFTIRQ delta to rq->curr's groups
> as PSI_IRQ_FULL pressure stall. And per-cpu IRQ stall can also get from psi_system.
>