On Mon, Feb 10, 2014 at 07:12:03PM +0100, Nicholas Mc Guire wrote: > On Mon, 10 Feb 2014, Peter Zijlstra wrote: > > > On Mon, Feb 10, 2014 at 06:17:12PM +0100, Nicholas Mc Guire wrote: > > > maybe I'm missing/missunderstanding something here but > > > pi_unlock -> arch_spin_unlock is a full mb() > > > > Nope, arch_spin_unlock() on x86 is a single add[wb] without LOCK prefix. > > > > The lock and unlock primitives are in general specified to have ACQUIRE > > resp. RELEASE semantics. > > > > See Documentation/memory-barriers.txt for far too much head-hurting > > details. > > I did check that - but from the code check it seems to me to be using a > lock prefix in the fast __add() path and an explicit smp_add() in the slow > path (arch/x86/include/asm/spinlock.h:arch_spin_unlock) the __add from > arch/x86/include/asm/cmpxchg.h does lock or am I missinterpreting this ? > the other archs I believe were all doing explicit mb()/smp_mb() in the > arch_spin_unlock - will go check this again. It uses UNLOCK_LOCK_PREFIX, which if you look carefully, is normally always "". Only some 'broken' i386 chips require a LOCK there. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
