On 4/3/21 9:51 pm, Filipe Laíns wrote: > On Thu, 2021-03-04 at 21:33 +1000, Allan McRae via arch-dev-public wrote: >> On 3/3/21 10:54 am, Allan McRae via arch-dev-public wrote: >>> On 2/3/21 9:51 pm, Allan McRae wrote: >>>> Hi all, >>>> >>>> A new RFC has been opened here: >>>> https://gitlab.archlinux.org/archlinux/rfcs/-/merge_requests/2 >>>> >>>> Summary: >>>> Make -march=x86_64-v2 the default for our packages. This assumes the >>>> following instruction sets which are essentially available on all but >>>> the oldest AMD CPUs: >>>> >>>> CMPXCHG16B, LAHF-SAHF, POPCNT, SSE3, SSE4.1, SSE4.2, SSSE3 >>>> >>>> Please visit the above link for discussion. >> >> Lets put discussion on this RFC on hold for a while. Clearly there is a >> reasonable amount of objection to making x86-64-v2 the default. While >> this mostly appears to be objection based on personal circumstances and >> not on the basis of whether this change is good for the distro, I will >> work within these limits. >> >> A lot of comments have suggested adding x86-64-v2 and -v3 as additional >> architectures instead. I will revamp the the proposal to take that >> approach. Though, to do this automated would require more work it may >> be the push we need for a signing enclave to be set up. >> >> Allan > > Thank you. Though, I find this a bit dismissive of my feedback arguing that > this > would very likely not have any significant effect whatsoever in performance, > and > that it fails to solve the ISA extensions issue we have. While there was some > feedback based on personal circumstances, I provided objective argumentation > about how the proposal as is is probably not a good idea and not the best path > forward.
As I said, I am reworking the RFC, so your comments are not ignored but instead just not addressed yet. You are correct that a lot of software where the gains are biggest already provide optimized paths. But there are still gains to be had, and not just in performance. When I recompiled my system with something similar to x86-64-v3, I gained significant battery life on my laptop on daily use. The power saving is likely more noticealbe than speed gains. As part of the updated RFC, I will get some benchmarks included. And I know some packages have multiple variants provided with different optimization level. But the user needs to find them to use them. Looking a pkgstats, that may happen for a decent proportion of tensorflow users, but the other packages not so much. And there are issues with discoverability, and choice of optimization levels. Allan
