linux-kernel - Re: [Ksummit-2008-discuss] Delayed interrupt work, thread pools

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Date:	Thu, 03 Jul 2008 07:00:09 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	ksummit-2008-discuss@...ts.linux-foundation.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Jeremy Kerr <jk@...abs.org>
Subject: Re: [Ksummit-2008-discuss] Delayed interrupt work, thread pools


> If you really need the full scheduling capabilities of threads, then it
> sounds like a threadpool is all you need (and we should just provide a
> unified interface).

That's my thinking nowadays.

> Initially you were implying you'd prefer some type of non blockable
> workqueue (i.e. a workqueue that shifts to the next work item when and
> earlier item blocks).

That's also something I had in mind, I was tossing ideas around and
collecting feedback :-)

>    I can see this construct being useful because it
> would have easier to use semantics and be more lightweight than a full
> thread spawn.  It strikes me we could use some of the syslets work to do
> this ... 

Precisely what I had in mind.

> all the queue needs is an "next activation head", which will be
> the next job in the queue in the absence of blocking.  When a job
> blocks, syslets informs the workqueue and it moves on to the work on the
> "next activation head".  If a prior job unblocks, syslets informs the
> queue and it moves the "next activation head" to the unblocked job.
> What this is doing is implementing a really simple scheduler within a
> single workqueue, which I'm unsure is actually a good idea since
> schedulers are complex and tricky things, but it is probably worthy of
> discussion.

The question is: is that significantly less overhead than just spawning
a new full blown kernel thread ? enough to justify the complexity ? at
the end of the day, it means allocating a stack (which on ppc64 is still
16K, I know it sucks)... 

Ben.

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