Chen, Kenneth W wrote:
Nick Piggin wrote on Thursday, March 30, 2006 6:53 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. You guys (ia64) are the ones who want to introduce a new interface, because you think conforming to the kernel's current interfaces will be too costly. I simply suggested a way you could do this that would have a chance of being merged. If you want to change the semantics of smp_mb__*, then good luck auditing all that well documented code that uses it. I just happen to think your best bet is to stick with the obvious full barrier semantics (which is what other architectures, eg powerpc do), and introduce something new if you want more performance. -- SUSE Labs, Novell Inc.Send instant messages to your online friends http://au.messenger.yahoo.com -
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