Re: [patch] x86_64, irq: check remote IRR bit before migrating level triggered irq

["Siddha, Suresh B" <suresh.b.siddha@intel.com>]

On Fri, May 18, 2007 at 11:28:25AM -0700, Yinghai Lu wrote:
> On 5/18/07, Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> >
> > If the vector number stays same during irq migration and if we reset remote
> > IRR bit using the above method(edge and then back to level) during
> > irq migration, then we have a problem. A new interrupt arriving on a new
> > cpu will set the remote IRR bit and now the old inflight EOI broadcast
> > reaches IOAPIC RTE(resetting the remote IRR bit, because the vector in the
> > broadcast msg is same), while the kernel code still assumes that the remote
> > IRR bit is still set. This will lead to more problems and issues.
> 
> coud add some line __assign_irq_vector. to make sure old_vector!=vector.

hmm..
what happens when there is second(and very quick) irq migration which brings the
irq back to old cpu(or to a third cpu) with old vector.

Point is, we are not taking care of the inflight messages(which can perhaps,
theoretically, can get delayed for long time)

thanks,
suresh