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authorDavid Howells <dhowells@redhat.com>2006-06-10 09:54:12 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-10 11:02:05 -0700
commit670bd95e0413c43f878b73a4a3919d1f452a4157 (patch)
treedb7b05810c5cc61c89b856996174e31147611cba /include/asm-h8300
parentd90d2c385d4d832428d1e51c2a7edeef39c822f5 (diff)
[PATCH] Further alterations for memory barrier document
From: David Howells <dhowells@redhat.com> Apply some alterations to the memory barrier document that I worked out with Paul McKenney of IBM, plus some of the alterations suggested by Alan Stern. The following changes were made: (*) One of the examples given for what can happen with overlapping memory barriers was wrong. (*) The description of general memory barriers said that a general barrier is a combination of a read barrier and a write barrier. This isn't entirely true: it implies both, but is more than a combination of both. (*) The first example in the "SMP Barrier Pairing" section was wrong: the loads around the read barrier need to touch the memory locations in the opposite order to the stores around the write barrier. (*) Added a note to make explicit that the loads should be in reverse order to the stores. (*) Adjusted the diagrams in the "Examples Of Memory Barrier Sequences" section to make them clearer. Added a couple of diagrams to make it more clear as to how it could go wrong without the barrier. (*) Added a section on memory speculation. (*) Dropped any references to memory allocation routines doing memory barriers. They may do sometimes, but it can't be relied on. This may be worthy of further documentation later. (*) Made the fact that a LOCK followed by an UNLOCK should not be considered a full memory barrier more explicit and gave an example. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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