[1/4] RFC: SLB rewrite (core rewrite)

[David Gibson]

On Sun, Jul 11, 2004 at 10:27:46AM +1000, Anton Blanchard wrote:
>
>
> > This branch probably shouldn't be predicted.  The general rule on branch
> > prediction is for an error case, or a missed lock.  Since about power 4,
> > the branch prediction is a little over 99% correct, you'll get a miss 1
> > out of 62 times or 1.6% of the time.  It's probably not measurable, just
> > might save a few cycles.
>
> Milton and I looked over this a while ago. Neither of the two POWER4
> branch prediction algorithms will do a good job. We are likely to get 2
> mispredictions per loop whereas we only get one misprediction per loop
> with static prediction.
>
> As David pointed out we have removed the slbmfee loop completely in
> subsequent patches.

Well.. we did some timings with a hacky patch which just took out the
slbmfee on the grounds that most of the time it would just work.  I
have a patch to actually safely remove it by bolting the kernel stack
into SLB slot 1, but I'm not yet sure how to get that working properly
on iSeries.

--
David Gibson			| For every complex problem there is a
david AT gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.
http://www.ozlabs.org/people/dgibson

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