Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RFC PATCH] workqueue: Unbind workers before sending them to exit() | Date | Tue, 26 Jul 2022 21:36:06 +0100 |
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On 26/07/22 07:30, Tejun Heo wrote: > Hello, > > On Mon, Jul 25, 2022 at 11:21:37AM +0100, Valentin Schneider wrote: >> Hm so my choice of words in the changelog wasn't great - "initial setup" >> can be kernel init, but *also* setup of whatever workload is being deployed >> onto the system. >> >> So you can be having "normal" background activity (I've seen some IRQs end >> up with schedule_work() on isolated CPUs, they're not moved away at boot >> time but rather shortly before launching the latency-sensitive app), some >> preliminary stats collection / setup to make sure the CPU will be quiet >> (e.g. refresh_vm_stats()), and *then* the application starts with >> fresh-but-no-longer-required extra pcpu kworkers assigned to its CPU. > > Ah, I see. I guess we'll need to figure out how to unbind the workers then. >
I've been playing with different ways to unbind & wake the workers in a sleepable context, but so far I haven't been happy with any of my experiments.
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.
If any of that sounds ludicrous please shout, otherwise I'm going to keep tinkering :)
> Thanks. > > -- > tejun
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