On Tue, Apr 22, 2008 at 12:50:30PM -0700, Linus Torvalds wrote:
>
>
> On Tue, 22 Apr 2008, Ingo Molnar wrote:
> >
> > ok. In which case the reschedule vector could be consolidated into that
> > as well (it's just a special single-CPU call). Then there would be no
> > new vector allocations needed at all, just the renaming of
> > RESCHEDULE_VECTOR to something more generic.
>
> Yes.
>
> Btw, don't get me wrong - I'm not against multiple vectors per se. I just
> wonder if there is any real reason for the code duplication.
>
> And there certainly *can* be tons of valid reasons for it. For example,
> some of the LAPIC can only have something like two pending interrupts per
> vector, and after that IPI's would get lost.
>
> However, since the queuing is actually done with the data structures, I
> don't think it matters for the IPI's - they don't need any hardware
> queuing at all, afaik, since even if two IPI's would be merged into one
> (due to lack of hw queueing) the IPI handling code still has its list of
> events, so it doesn't matter.
>
> And performance can be a valid reason ("too expensive to check the shared
> queue if we only have per-cpu events"), although I$ issues can cause that
> argument to go both ways.
>
> I was also wondering whether there are deadlock issues (ie one type of IPI
> has to complete even if a lock is held for the other type).
>
> So I don't dislike the patch per se, I just wanted to understand _why_ the
> IPI's wanted separate vectors.
The "too expensive to check the shared queue" is one aspect of it. The
shared queue need not have events *for us* (at least, unless Jens has
changed the implementation a bit) but it can still have events that we
would need to check through.
I don't think deadlock is a problem (any more than with multiple vectors).
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
