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

[David Woodhouse]

On Tue, 2009-01-20 at 13:38 +0100, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@xxxxxxx> 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@xxxxxxxxx                              Intel Corporation

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