On Sun, May 13, 2007 at 07:26:13PM -0400, Bill Davidsen wrote:By optimal you seem to mean "generate fewer CPU cycles by risking use of an obsolete value," while by the same term I mean read the correct and current value from the memory location without the overhead of locks. If your logic doesn't require the correct value, why read it at all? And if it does, how fewer cycles and cache impact can anything have than a single register load from memory?
Krzysztof Halasa wrote:
Robert Hancock <hancockr@xxxxxxx> writes:
You don't need volatile in that case, rmb() can be used.
rmb() invalidates all compiler assumptions, it can be much slower.
It does not invalidate /all/ assumptions.
Yes, why would you use rmb() when a read of a volatile generates optimal code?
Read of a volatile is guaranteed to generate the least optimal code.
That's what volatile does, guarantee no optimization of that particular
access.