On 04/19/2010 02:19 PM, Peter Zijlstra wrote:
Still have two cmpxchgs in the common case. The first iteration will fail, fetching last_value, the second will work. It will be better when we have contention, though, so it's worthwhile.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); do { if (ret< last) return last; last = atomic64_cmpxchg(&last_value, last, ret); } while (unlikely(last != ret)); Or so.
Yes, looks optimal when !NONSTOP_TSC. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
