Dear Julie.... On Tue, Aug 2, 2011 at 04:28, Julie Sullivan <kernelmail.jms@xxxxxxxxx> wrote: > Specifically, the conditional > > if (t->rcu_read_lock_nesting == 0 && > unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > rcu_read_unlock_special(t); > > I've googled for 'likely/unlikely' and i've seen > > if (unlikely(... > > before in kernel code, and I might understand if the logical operator > here were || not &&, but why is the 'unlikely' attribute only applied > to the second operand here? i guess that's because first condition "t->rcu_read_lock_nesting == 0" has about 50%-50% chance.... so putting likely() or unlikely() has no use here... i read somewhere (or maybe someone's opinion) that you only use likely() or unlikely() if you are about above 90% (or maybe...if possible 99%) sure that condition will be true or false....otherwise, avoid likely()/unlikely() and let the compiler+processor do the usual ordering/branch prediction. just my 2 cents... -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
