linux-kernel - Re: [PATCH 03/19] scheduler: implement workqueue scheduler class

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Date:	Thu, 1 Oct 2009 09:57:37 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
cc:	jeff@...zik.org, mingo@...e.hu, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com
Subject: Re: [PATCH 03/19] scheduler: implement workqueue scheduler class

On Thu, 1 Oct 2009, Tejun Heo wrote:
>
> Implement workqueue scheduler class.  Workqueue sched_class inherits
> fair sched_class and behaves exactly the same as sched_class except
> that it has two callback functions which get called when a task is put
> to sleep and wakes up and doesn't allow switching to different
> scheduler class.

So this looks odd to me.

I agree completely with the callback functions, but what I don't agree 
with is that this is somehow workqueue-related. I bet that others could 
use this, and in fact, I suspect that it should not be tied to the 
scheduler class at all, but to the _thread_.

Just as an example, I could imagine that we would do lock_kernel() 
releasing the kernel lock on scheduling (and re-taking it on wakeup) as a 
callback. Or async IO handling - both done independently of any 
"workqueue" logic.

So tying this to the scheduler class seems a bit odd. But maybe I'm 
missing something?

		Linus
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