linux-kernel - 回复: Question on workqueue: Manually break affinity on hotplug

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Message-ID: <BYAPR11MB263266CF64A8EE2A91B979E5FFA50@BYAPR11MB2632.namprd11.prod.outlook.com>
Date:   Sun, 17 Jan 2021 10:16:23 +0000
From:   "Zhang, Qiang" <Qiang.Zhang@...driver.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "laijs@...ux.alibaba.com" <laijs@...ux.alibaba.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 回复: Question on   workqueue: Manually break affinity on hotplug

Hello Peter, Lai

Sorry to disturb again, I'm still confused, when the CPU is offline, we active  call set_cpus_allowed_ptr function  to reset per-cpu kthread cpumask,
in sched_cpu_dying function , migrate_tasks function will reset per-cpu kthread's cpumask on runq, even if not on runq, when wake up,  other online CPUs will also be selected to run.

what I want to ask is why we take the initiative to set it up?

Thanks
Qiang


________________________________________
发件人: Peter Zijlstra <peterz@...radead.org>
发送时间: 2021年1月14日 17:11
收件人: Zhang, Qiang
抄送: linux-kernel@...r.kernel.org
主题: Re: Question on   workqueue: Manually break affinity on hotplug

[Please note this e-mail is from an EXTERNAL e-mail address]

On Thu, Jan 14, 2021 at 08:03:23AM +0000, Zhang, Qiang wrote:
> Hello Peter
>
> Excuse me, I have some questions for you, about a description of this change:
>
> ''Don't rely on the scheduler to force break affinity for us -- it will
> stop doing that for per-cpu-kthreads."
>
> this mean when cpuhotplug, scheduler do not  change  affinity for per-cpu-kthread's task, if we not active setting affinity?
> but if per-cpu-kthread's task is not run state, when wake up,  will reset it's affinity, this  is done automatically.
>
> or is it,  this place modified to fit the new one hotplug mechanism which
> ("sched/hotplug: Consolidate task migration on CPU unplug")?

https://lkml.kernel.org/r/20201214155457.3430-1-jiangshanlai@gmail.com
https://lkml.kernel.org/r/20201218170919.2950-1-jiangshanlai@gmail.com
https://lkml.kernel.org/r/20201226025117.2770-1-jiangshanlai@gmail.com
https://lkml.kernel.org/r/20210111152638.2417-1-jiangshanlai@gmail.com
https://lkml.kernel.org/r/20210112144344.850850975@infradead.org