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SubjectRe: [PATCH][RFC] per isr in_progress markers
Linus Torvalds wrote:
> On Sun, 8 Sep 2002, Zwane Mwaikambo wrote:
>
>>Here is a newer (untested) patch incorporating Ingo's suggestions as well
>>as adding an extra request_irq flag so that isrs can use isr_unmask_irq()
>>to enable their interrupt lines.
>
>
> Hmm.. I really don't get the point of what this is supposed to actually
> help.
>
> Clearly, if the device doesn't share the irq line, this doesn't matter.
> Similarly, it shouldn't matter if there is just one device that is active
> (ie irq line sharing with some slow device where the interrupt happens
> fairly seldom).
>
> As far as I can tell, the only time when this might be an advantage is an
> SMP machine with multiple devices sharing an extremely busy irq line. Then
> the per-isr in-progress bit allows multiple CPU's to actively handle
> several of the devices at the same time.


IMO one should seek to avoid sharing an IRQ line at all. I dunno that
you really want to tune for that case, when the user could vastly
improve the situation by manipulating IRQs in BIOS setup or similar
IRQ-distribution methods.

On an SMP box you especially want to distribute irqs to take best
advantage of irq affinity.

Jeff


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