On 04/19/2010 05:32 PM, Glauber Costa wrote:
Right, another option is to put the initial read outside of the loop,
that way you'll have the best of all cases, a single LOCK'ed op in the
loop, and only a single LOCK'ed op for the fast path on sensible
architectures ;-)
last = atomic64_read(&last_value);
isn't a barrier enough here?
No. On i386, the statement
last = last_value;
will be split by the compiler into two 32-bit loads. If a write
(atomic, using cmpxchg) on another cpu happens between those two loads,
then the variable last will have a corrupted value.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
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