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

[Leon Woestenberg]

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@xxxxxxxxxxxxxx> wrote:
> Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> 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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