On Sat, 16 Feb 2008 18:33:16 +0100 Willy Tarreau <[EMAIL PROTECTED]> wrote:
> On Sat, Feb 16, 2008 at 09:25:52AM -0800, Arjan van de Ven wrote: > > On Sat, 16 Feb 2008 17:08:01 +0100 > > Roel Kluin <[EMAIL PROTECTED]> wrote: > > > > > The patch below was not yet tested. If it's correct as it is, > > > please comment. --- > > > Fix Unlikely(x) == y > > > > > > > you found a great set of bugs.. > > but to be honest... I suspect it's just best to remove unlikely > > altogether for these cases; unlikely() is almost a > > go-faster-stripes thing, and if you don't know how to use it you > > shouldn't be using it... so just removing it for all wrong cases is > > actually the best thing to do imo. > > Well, eventhough the author may not know how to use it, "unlikely" at > least indicates the intention of the author, or his knowledge of what > should happen here. I'd suggest leaving it where it is because the > authot of this code is in best position to know that this branch is > unlikely to happen, eventhough he does not correctly use the macro. > you have more faith in the authors knowledge of how his code actually behaves than I think is warranted :) Or faith in that he knows what "unlikely" means. I should write docs about this; but unlikely() means: 1) It happens less than 0.01% of the cases. 2) The compiler couldn't have figured this out by itself (NULL pointer checks are compiler done already, same for some other conditions) 3) It's a hot codepath where shaving 0.5 cycles (less even on x86) matters (and the author is ok with taking a 500 cycles hit if he's wrong) If you think unlikely() means something else, we should fix what it maps to towards gcc ;) (to.. be empty ;) -- If you want to reach me at my work email, use [EMAIL PROTECTED] For development, discussion and tips for power savings, visit http://www.lesswatts.org _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
