From: Kees Cook > Sent: Friday, August 18, 2023 9:25 PM > > On Fri, Aug 18, 2023 at 04:10:49PM -0400, Jeff Layton wrote: > > [...] > > extra checks (supposedly) compile down to nothing. It should be possible > > to build alternate refcount_t handling functions that are just wrappers > > around atomic_t with no extra checks, for folks who want to really run > > "fast and loose". > > No -- there's no benefit for this. We already did all this work years > ago with the fast vs full break-down. All that got tossed out since it > didn't matter. We did all the performance benchmarking and there was no > meaningful difference -- refcount _is_ atomic with an added check that > is branch-predicted away. Hmmm IIRC recent Intel x86 cpu never do static branch prediction. So you can't avoid mis-predicted branches in cold code. David > Peter Zijlstra and Will Deacon spent a lot of > time making it run smoothly. :) > > -Kees > > -- > Kees Cook - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
