Generic IOMMU pooled allocator

chase rayfield cusbrar1 at
Tue Mar 24 10:29:31 AEDT 2015

On Mar 23, 2015 7:13 PM, "Sowmini Varadhan" <sowmini.varadhan at>
> On (03/24/15 09:21), Benjamin Herrenschmidt wrote:
> >
> > So we have two choices here that I can see:
> >
> >  - Keep that old platform use the old/simpler allocator
> Problem with that approach is that the base "struct iommu" structure
> for sparc gets a split personality: the older one is used with
> the older allocator, and other ugly things ensue.  (alternatively,
> you end up duplicating a version of the code with the flush_all
> inlined).
> >  - Try to regain the bulk of that benefit with the new one
> >
> > Sowmini, I see various options for the second choice. We could stick to
> > 1 pool, and basically do as before, ie, if we fail on the first pass of
> > alloc, it means we wrap around and do a flush, I don't think that will
> > cause a significant degradation from today, do you ? We might have an
> > occasional additional flush but I would expect it to be in the noise.
> Isn't this essentially what I have in patch v5 here:
> (the ops->reset is the flushall indirection, can be renamed if the
> latter is preferred)
> > Dave, what's your feeling there ? Does anybody around still have some
> > HW that we can test with ?
> I actually tested this on a V440 and a ultra45 (had a heck of a
> time finding these, since the owners keep them turned off because
> they are too noisy and consume too much power :-).

So we need tests then more than hw?.... I have an ultra1, ultra10 and t2000
I can test on if needed. And I'd appreciate my caches not being flushed
excessively on these boxes :-) too. I'll see if I can't get Gentoo on the
u10 tonight.

Also... It would be more "green" to make the code run faster on these boxes
than otherwise!
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