Messages in this thread | | | Date | Sat, 08 Apr 2006 08:10:38 -0600 | From | Robert Hancock <> | Subject | Re: [PATCH 2.6.16] Shared interrupts sometimes lost |
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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/
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