Re: [PATCH][RFC] per isr in_progress markers

[Jeff Garzik <jgarzik@mandrakesoft.com>]

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