On 02/16/2008 09:42 AM, Arjan van de Ven wrote: > 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 ;)
Well, I didn't consider what today's compiler does, but used it as a general indicator, because I think that code will be around a long time. If you show me some test results that prove it causes harm I might consider removing it. -Geoff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
