Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

David Woodhouse
2009-01-20T19:50:36Z

On Tue, 2009-01-20 at 13:38 +0100, Ingo Molnar wrote:
>
> * Nick Piggin <npiggin@suse.de> wrote:
>
> > > > it seems like a nice opt-in thing that can be used where the aliases
> > > > are verified and the code is particularly performance critical...
> > >
> > > Yes. I think we could use it in the kernel, although I'm not sure how
> > > many cases we would ever find where we really care.
> >
> > Yeah, we don't tend to do a lot of intensive data processing, so it is
> > normally the cache misses that hurt most as you noted earlier.
> >
> > Some places it might be appropriate, though. It might be nice if it can
> > bring code size down too...
>
> I checked, its size effects were miniscule [0.17%] on the x86 defconfig
> kernel and it seems to be a clear loss in total cost as there would be an
> ongoing maintenance cost

They were talking about 'restrict', not strict-aliasing. Where it can be
used, it's going to give you optimisations that strict-aliasing can't.

--
David Woodhouse Open Source Technology Centre
David.Woodhouse@intel.com Intel Corporation