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How likely should likely() be?How likely should likely() be?Posted Feb 12, 2004 13:33 UTC (Thu) by zooko (subscriber, #2589)Parent article: How likely should likely() be? Can GCC's profile-directed optimization be used on the kernel? If so, you would think that this would obviate the need for programmer-specified hints in the source code.
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How likely should likely() be? Posted Feb 14, 2004 20:48 UTC (Sat) by giraffedata (subscriber, #1954) [Link] Except that programmer-specified hints are a lot easier. Also, the hint to the code reader can be valuable too. Where the code reader is concerned, the likely() notation is awful. I read this as "if some_condition is likely, then ..." A more appropriate notation would be assert(likely(some_condition)); if (some_condition) ... Furthermore, just minimizing the average time spent doing the branch isn't the only reason to do branch prediction hints. Consider if (fast_response_required) ... Even if fast_response_required is rarely true, I may want the code optimized for the case that it is. That gets me to optimize_for(fast_response_required)or maybe
if (fast_response_required) {
optimize_for_this_case();
}
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