On Tue, 29 Nov 2022, Jiri Slaby wrote:
On 28. 11. 22, 20:10, Michal Such?nek wrote:
Yes, sorry - I was meant to say that the -v3 improvement is more obvious because AVX widens the vectors. -v2 only is going to improve more specific vectorizable workloads while -v3 is going to improve most vectorizable workloads.
As in compilling the whole distro for -v2 does not provide appreciable benefits because most of the specific workloads that benefit a lot from sse already use it in one way or another, and compiling general purpose code with it gives mixed results (as far as the few banchmarks provided show).
So can someone explain me at last why it was decided Leap/ALP adopts this then? It makes no sense to me. Neither performance-wise (there is almost no diff), nor maintenance-wise (there is almost no diff).
It was first decided to go with -v3 but then backtracked to -v2 for a variety of FUD & technical reasons. That there is Factory-First and the close ALP/Leap relationship didn't help of course. Anyway, I kind-of agree that -v2 doesn't make much sense on its own but at least some advancement over x86-64 makes sense (for atomics and other minor details), but since there's no -v1.5 there's not much choice here (and yes, -v2 is kind of arbirtrary). I think that even defaulting to -v2 is going to help some ISVs (since RHEL 9 now requires x86-64-v2), both in compatibility and performance. Richard. -- Richard Biener <rguenther@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)