On Thu, May 31, 2007 at 07:50:58AM -0600, Eric W. Biederman wrote: > > On x86_64 kernel, level triggered irq migration gets initiated in the context > of that interrupt(after executing the irq handler) and following steps are > followed to do the irq migration. > > 1. mask IOAPIC RTE entry; // write to IOAPIC RTE > 2. EOI; // processor EOI write > 3. reprogram IOAPIC RTE entry // write to IOAPIC RTE with new destination and > // and interrupt vector due to per cpu vector > // allocation. > 4. unmask IOAPIC RTE entry; // write to IOAPIC RTE > > Because of the per cpu vector allocation in x86_64 kernels, when the irq > migrates to a different cpu, new vector(corresponding to the new cpu) will > get allocated. > > An EOI write to local APIC has a side effect of generating an EOI write > for level trigger interrupts (normally this is a broadcast to all IOAPICs). > The EOI broadcast generated as a side effect of EOI write to processor may > be delayed while the other IOAPIC writes (step 3 and 4) can go through. > > Normally, the EOI generated by local APIC for level trigger interrupt > contains vector number. The IOAPIC will take this vector number and > search the IOAPIC RTE entries for an entry with matching vector number and > clear the remote IRR bit (indicate EOI). However, if the vector number is > changed (as in step 3) the IOAPIC will not find the RTE entry when the EOI > is received later. This will cause the remote IRR to get stuck causing the > interrupt hang (no more interrupt from this RTE). > > Current x86_64 kernel assumes that remote IRR bit is cleared by the time > IOAPIC RTE is reprogrammed. Fix this assumption by checking for remote IRR > bit and if it still set, delay the irq migration to the next interrupt > arrival event(hopefully, next time remote IRR bit will get cleared > before the IOAPIC RTE is reprogrammed). > > Initial analysis and patch from Nanhai. > > Clean up patch from Suresh. > > Rewritten to be less intrusive, and to contain a big fat comment by Eric.
Acked-by: Suresh Siddha <[EMAIL PROTECTED]> Thanks Eric. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
