Re: [PATCH 00/10] workqueue: break affinity initiatively

[Peter Zijlstra]

On Mon, Dec 14, 2020 at 11:54:47PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> 
> 06249738a41a ("workqueue: Manually break affinity on hotplug")
> said that scheduler will not force break affinity for us.
> 
> But workqueue highly depends on the old behavior. Many parts of the codes
> relies on it, 06249738a41a ("workqueue: Manually break affinity on hotplug")
> is not enough to change it, and the commit has flaws in itself too.
> 
> We need to thoroughly update the way workqueue handles affinity
> in cpu hot[un]plug, what is this patchset intends to do and
> replace the Valentin Schneider's patch [1].

So the actual problem is with per-cpu kthreads, the new assumption is
that hot-un-plug will make all per-cpu kthreads for the dying CPU go
away.

Workqueues violated that. I fixed the obvious site, and Valentin's patch
avoids workqueues from quickly creating new ones while we're not
looking.

What other problems did you find?