lkml.org 
[lkml]   [2008]   [Jul]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Ksummit-2008-discuss] Delayed interrupt work, thread pools
Leon Woestenberg wrote:
> Hello,
>
> (including linux-rt-users in the CC:, irqthreads are on-topic there)

Actually it's probably not interesting for this case.

>
> On Wed, Jul 2, 2008 at 1:02 PM, Andi Kleen <andi@firstfloor.org> wrote:
>> Benjamin Herrenschmidt <benh@kernel.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

I described this case. If the interrupt handler blocks for a long
time (as Ben asked for) then the interrupts will not be handled
for a long time. Probably not what you want.

BTW this was not a criticsm of rt linux (in whose context
irqthreads make sense as I explained) , just an explanation why they
imho don't make sense (IMHO) in a non hard rt interruptible kernel
and especially not to solve Ben's issue.

>
>> 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.

It was a general description of all possible irqthreads.

-Andi


\
 
 \ /
  Last update: 2008-07-02 13:27    [W:0.050 / U:0.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site