Re: [PATCH 2.6.16] Shared interrupts sometimes lost

[Robert Hancock <hancockr@shaw.ca>]

Neil Brown wrote:
>  However there is room for a race here.  If an event occurs between
>  the read and the write, then this will NOT de-assert the IRQ line.
>  It will remain asserted throughout.
> 
>  Now if the IRQ is handled as an edge-triggered line (which I believe
>  they are in Linux), then losing this race will mean that we don't see
>  any more interrupts on this line.

PCI interrupts should always be level triggered, not edge triggered 
(except maybe in a few special cases - non-native-mode PCI IDE maybe? 
and in those cases I don't think the interrupt is considered sharable). 
With a level triggered interrupt the ISR will simply be triggered again 
and the event handled in this case so there is no race. I think this 
patch is going to double interrupt overhead and only covers up some 
other problem.

I think that in cases where the interrupt is edge triggered and is 
shared (for example on ISA cards that support it) the kernel already has 
such logic as you describe.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/