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On Fri, 5 Aug 2022, Nikolai Nikolaevskii wrote:
dieter wrote:
Thus I would propose raising the x86_64 architecture level to x86-64-v2 for openSUSE Factory. v2 requires CMPXCHG16B, [SL]AHF, POPCNT and SSE4_2 (and the predecessor SSE extensions) but not AVX, BMI or FMA. ... Comments welcome. Hi, Are there some data available about the actual benefit of this change? Therefore I think it would really be important to have some data about
On Thu, 28 Jul 2022 11:44:03 +0000 (UTC) Richard Biener wrote: the expected benefits for standard use cases on -v2 or -v3 CPUs.
https://openbenchmarking.org/result/2103142-HA-UARCHLEVE55 Only x86-64-v3 has good gains (sometimes).
Only AVX with x86-64-v3 has the chance to double throughput of vectorized code, plus -v3 has BMI which can make differences in crypto and hashing. But as it is always with bechmarks - if you get to choose it you can choose the outcome of the experiment. There's definitely special cases benefiting of SSE 4.2 but the gain with -v2 is expected to be limited compared to -v3, but -v3 is understood to be a no-go for openSUSE. I'll note that while some specialized libraries come with separate code paths for ISAs they benefit from and appropriately dispatch via CPUid most developers are simply too lazy to even think about that. You may say that performance may not matter in most cases but performance often also translates to less energy use which for mobile uses might be even more important than performance (but that's even more difficult to measure, of course). 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)