* David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > 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. the two are obviously related (just that the 'restrict' keyword can be used for same-type pointers so it gives even broader leeway) so i used the 0.17% figure i already had to give a ballpark figure about what such type of optimizations can bring us in general. (Different-type pointer uses are a common pattern: we have a lot of places where we have pointers to structures with different types so strict-aliasing optimization opportunities apply quite broadly already.) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
