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

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Date:	Wed, 2 Jul 2008 13:19:39 +0200
From:	"Leon Woestenberg" <leon.woestenberg@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	benh@...nel.crashing.org,
	"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>, RT <linux-rt-users@...r.kernel.org>
Subject: Re: [Ksummit-2008-discuss] Delayed interrupt work, thread pools

Hello,

(including linux-rt-users in the CC:, irqthreads are on-topic there)

On Wed, Jul 2, 2008 at 1:02 PM, Andi Kleen <andi@...stfloor.org> wrote:
> Benjamin Herrenschmidt <benh@...nel.crashing.org> writes:
>
>>> how much of this would be obsoleted if we had irqthreads ?
>>
>> I'm not sure irqthreads is what I want...
>>
> I also think interrupts threads are a bad idea in many cases because
> their whole "advantage" over classical interrupts is that they can
> block. Now blocking can be usually take a unbounded potentially long
> time.
>
> What do you do when there are more interrupts in that unbounded time?
>
If by irqthreads the -rt implementation is meant, isn't this what happens:

irq kernel handler masks the source interrupt
irq handler awakes the matching irqthread (they always are present)
irqthread is scheduled, does work and returns
irq kernel unmasks the source interrupt

> Create more interrupt threads?  At some point you'll have hundreds
> of threads doing nothing when you're unlucky.
>
Each irqthread handles one irq.
So now new irq thread would spawn for any interrupt.

Regards,
-- 
Leon
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