Hi, On 2024-02-09 13:19:49 +0500, Andrey M. Borodin wrote: > > On 8 Feb 2024, at 06:52, Nathan Bossart <nathandboss...@gmail.com> wrote: > > For the same compASC() test, I see an ~8.4% improvement with your int64 > > code and a ~3.4% improvement with this: > > If we care about branch prediction in comparison function, maybe we could > produce sorting that inlines comparator, thus eliminating function call to > comparator? We convert comparison logic to int, to extract comparison back > then.
We have some infrastructure for that actually, see sort_template.h. But perhaps we should define a static inline of the generic pg_qsort() even. OTOH, plenty places that'll just end up to a pointless amount of code emitted to sort ~5 elements on average. > I bet “call" is more expensive than “if". Not really in this case. The call is perfectly predictable - a single qsort() will use the same callback for every comparison, whereas the if is perfectly *unpredictable*. A branch mispredict is far more expensive than a correctly predicted function call. Greetings, Andres
