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 14:13:02 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Abel Wu <wuyun.abel@...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 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.

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.

Thanks.

> 
> Abel