Re: [PATCH 0/1] Recurse when searching for empty slots inresources trees
From: Andrew Patterson
Date: Tue Jun 16 2009 - 19:35:58 EST
On Tue, 2009-06-16 at 16:05 -0700, Linus Torvalds wrote:
> On Tue, 16 Jun 2009, Andrew Patterson wrote:
> > That is at least one problem. I initially tried reparenting this stuff.
> > That is what got backed out in
> > http://thread.gmane.org/gmane.linux.kernel/768526/
> Well, aren't we in the exact same situation still? Ie the problem (as
> Matthew claims) is:
> 'Basically it was that we came across a machine with the opposite
> problem -- that we found a parent after we found a child (and claimed
> the child's resources), and had no way to insert the parent's region
> above the child's region. Alex's machine finds the child after the
> parent and needs to insert the child's resource inside the parent's
> and the problem is that anything that isn't explicitly aware of the
> topology is always going to be potentially confused about things like
> this, since it's not clear at which level you want to find or add a
> > > But you fix it by making find_resource always go as deep as it can (if I
> > > read the code correctly).
> > Well, just deep enough.
> Ok, color me confused now. When is "as deep as it can" different from your
> "just deep enough"?
Maybe confusion on what is meant by 'as deep as'. My patch continues
until it doesn't find a conflict including checking sub-children and
stops as soon as an appropriate resource is found that does not
conflict. Perhaps we mean the same thing.
> > Is there a reason that find_resources should stop at the roots immediate
> > child/sibling. It seems like a bug to me. Hence this patch.
> Well, find_resource() found room for a resource. So it returns it. The
> point is, your patch returns another - equally valid one.
I am confused. The existing code will return a conflict and bomb out.
> Now, I'm not saying that your patch is wrong, but I _am_ worried that it
> (once more) changes some random heuristic when we have two choices, and it
> just makes it choose the other choice.
> We've had those kinds of situations before. The thread you point to is an
> exact case of this. My point is that I'd rather try to _avoid_ any
> ambiguous cases, and try to solve it properly at a higher PCI level, where
> the ambiguity doesn't exist any more (because we'd explicitly take the
> actual bus topology into account).
> So your patch may fix a bug, but I'm pretty sure I've seen a patch from
> Ivan that should _also_ fix it, and that I would expect to do it not by
> just tweaking a fundamentally ambiguous case.
OK. I would be happy to test Ivan's patch.
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