Question on workqueue: Manually break affinity on hotplug

Question on workqueue: Manually break affinity on hotplug

[Zhang, Qiang]

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")?

Thanks
Qiang

 

 

Re: Question on workqueue: Manually break affinity on hotplug

[Peter Zijlstra]

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

回复: Question on workqueue: Manually break affinity on hotplug

[Zhang, Qiang]

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@infradead.org>
发送时间: 2021年1月14日 17:11
收件人: Zhang, Qiang
抄送: linux-kernel@vger.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