Nick Piggin wrote on Thursday, March 30, 2006 11:35 PM > > >The memory ordering that above combination should produce is a > > >Linux style smp_mb before the clear_bit. Not a release. > > > > Whoever designed the smp_mb_before/after_* clearly understand the > > difference between a bidirectional smp_mb() and a one-way memory > > ordering. If smp_mb_before/after are equivalent to smp_mb, what's > > the point of introducing another interface? > > > They are not. They provide equivalent barrier when performed > before/after a clear_bit, there is a big difference. The usage so far that I can see for smp_mb__before_clear_bit() clear_bit is to close a critical section with clear_bit. I will be hard impressed to see a usage that allows stuff follows clear_bit to pass clear_bit, but not to pass the smp_mb_before_xxx. <end of critical section> smp_mb_before_clear_bit clear_bit <begin other code> But if you stand on the ground of smp_mb_before_xxx protects clear_bit from occurring before the "end of critical section", then smp_mb_before is such a brain dead interface and it is another good reason for having an explicit ordering mode built into the clear_bit. - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|