path: root/Documentation/volatile-considered-harmful.txt
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2010-03-24Documentation/volatile-considered-harmful.txt: correct cpu_relax() documentationRussell King
cpu_relax() is documented in volatile-considered-harmful.txt to be a memory barrier. However, everyone with the exception of Blackfin and possibly ia64 defines cpu_relax() to be a compiler barrier. Make the documentation reflect the general concensus. Linus sayeth: : I don't think it was ever the intention that it would be seen as anything : but a compiler barrier, although it is obviously implied that it might : well perform some per-architecture actions that have "memory barrier-like" : semantics. : : After all, the whole and only point of the "cpu_relax()" thing is to tell : the CPU that we're busy-looping on some event. : : And that "event" might be (and often is) about reading the same memory : location over and over until it changes to what we want it to be. So it's : quite possible that on various architectures the "cpu_relax()" could be : about making sure that such a tight loop on loads doesn't starve cache : transactions, for example - and as such look a bit like a memory barrier : from a CPU standpoint. : : But it's not meant to have any kind of architectural memory ordering : semantics as far as the kernel is concerned - those must come from other : sources. Signed-off-by: Russell King <> Cc: <> Acked-by: Linus Torvalds <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
2008-07-26Documentation cleanup: trivial misspelling, punctuation, and grammar ↵Matt LaPlante
corrections. Cc: Randy Dunlap <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
2007-06-24"volatile considered harmful"Jonathan Corbet
Encourage developers to avoid the volatile type class in kernel code. Signed-off-by: Jonathan Corbet <> Signed-off-by: Jesper Juhl <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>