Re: [PATCH 2/11] x86: convert to generic helpers for IPI functioncalls

From: Ingo Molnar
Date: Tue Apr 22 2008 - 15:26:41 EST



* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> > yes and i gave in - Nick and Jens wants to do some crazy stuff and
> > they had the numbers. Here's the previous discussion:
> >
> > http://lkml.org/lkml/2008/2/27/125
>
> No, the previous discussion was about single *queues* vs single
> *vectors*.
>
> I agree unconditionally with the decision to use a separate per-cpu
> queue from the shared queue (in fact, I would argue that the "mask"
> code might want to notice when the mask is just a single CPU, and turn
> a mask request into a targeted request).
>
> But I wonder why we want to then have two IPI target vectors, when it
> would appear to be perfectly fine and cheap to have just a single
> vector that can handle both the per-cpu case and the shared queue case
> (since the thing would tend to be one or the other, not both).
>
> A single vector is still pefectly fine, if 99% of all usage cases are
> the targeted-to-a-single-cpu thing, because the shared queue will
> basically be empty (and you can test that without even taking any
> locks).

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.

Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/