Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RFC PATCH] workqueue: Unbind workers before sending them to exit() | Date | Wed, 27 Jul 2022 10:22:01 +0100 |
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On 27/07/22 16:55, Lai Jiangshan wrote: > On Wed, Jul 27, 2022 at 2:30 PM Lai Jiangshan <jiangshanlai@gmail.com> wrote: > >> > >> > > >> > > What hasn't changed much between my attempts is transferring to-be-destroyed >> > > kworkers from their pool->idle_list to a reaper_list which is walked by >> > > *something* that does unbind+wakeup. AFAIA as long as the kworker is off >> > > the pool->idle_list we can play with it (i.e. unbind+wake) off the >> > > pool->lock. >> > > >> > > It's the *something* that's annoying to get right, I don't want it to be >> > > overly complicated given most users are probably not impacted by what I'm >> > > trying to fix, but I'm getting the feeling it should still be a per-pool >> > > kthread. I toyed with a single reaper kthread but a central synchronization >> > > for all the pools feels like a stupid overhead. >> > >> > I think fixing it in the workqueue.c is complicated. >> > >> > Nevertheless, I will also try to fix it inside workqueue only to see >> > what will come up. >> >> I'm going to kind of revert 3347fc9f36e7 ("workqueue: destroy worker >> directly in the idle timeout handler"), so that we can have a sleepable >> destroy_worker(). >> > > It is not a good idea. The woken up manager might still be in > the isolated CPU. > > On Wed, Jul 27, 2022 at 6:59 AM Tejun Heo <tj@kernel.org> wrote: >> >> I mean, whatever works works but let's please keep it as minimal as >> possible. Why does it need dedicated kthreads in the first place? Wouldn't >> scheduling an unbound work item work just as well? >> > > Scheduling an unbound work item will work well.
I did play a bit with that yesterday (pretty much replacing the pool->idle_timer with a delayed_work) but locking discouraged me - it's quite easy to end up with a self-deadlock.
Now, I've slept over it and have a fresh cup of coffee, and it's been the least intrusive-looking change I've tried, so let me give that a shot again.
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