On Wed, Jun 16, 2021 at 12:01:29PM +0200, Hans de Goede wrote: > Hi, > > On 6/16/21 10:28 AM, Daniel P. Berrangé wrote: > > On Tue, Jun 15, 2021 at 05:34:02PM -0400, Neal Gompa wrote: > >> Hey all, > >> > >> Earlier this week, I was helping with processing features for openSUSE > >> Leap 15.4[1] and I discovered that they're planning on introducing > >> x86_64-v2 to openSUSE soon. The reference for this change was that > >> RHEL 9 is going to use x86_64-v2[2]. Additionally, other distributions > >> have been considering bumping up to v2 or v3[3][4]. > >> > >> Some cursory examination of the new x86_64 sublevels seem to indicate > >> that x86_64-v2 goes back to roughly 2007~2008, merely cutting off the > >> first couple of generations of x86_64 CPUs from Intel and AMD. I > >> personally don't have any computers that don't have support for > >> x86_64-v2 anymore. > > > > Yes, you loose primarily Intel Conroe and Penryn generations and > > AMD Opteron Gen 1 -> Gen 3. I doubt this is a significant portion > > of Fedora installs. > > > > Slight tangent but I find Fedora's approach to hardware somewhat > > at odds with our approach to software. > > > > On the one hand we portray our project as a place for cutting > > edge Linux software & innovation. > > > > On the other hand we hold back our software by trying to keep > > supporting long obsolete hardware. > > > > There is of course always a balance between bumping min hardware > > specs and the impact on maintainers & users, but I'm not convinced > > that we have the balance right in targeting our x86_64 baseline at > > the very first generation of 64-bit CPUs from 15 years ago. I can't > > imagine such old CPUs makes up a significant portion of our users. > > I don't know about that, all I can offer is my own anecdotal to > the contrary. Of the 7 PCs/laptops which are in more or less > daily use in our houshold 3 of them are still core2 duo systems. > > Once the core2 duo / amd64 machines came out we really started hitting > the point of diminishing returns wrt PC performance for day 2 day > use. For a lot of simple day2 day use there really is no reason > to replace and x86_64-v1 capable machines unless they are > actually broken. > > Perhaps more importantly though, is that there we are also very > much at the point where bumping the processor architecture > requirements also leads to strongly diminishing returns. > > Also see Mateusz Jończyk excellent reply in this thread, how > rebuilding packages for x86_64-v2 vs x86_64 results in a barely > measurable performance improvement. > > Of course there are some specific algorithms which greatly > benefit from sse4.2, but those typically benefit even more > from avx/avx2 which are not included in x86_64-v2; and often > libraries already contain avx optimized code-paths for this > which they automatically use where possible. > > You talk about we "hold back our software by trying to keep > supporting long obsolete hardware". Let me flip the question > can you provide hard proof, as in concrete numbers showing > significant improvements, that switching to x86_64-v2 > actually buys us anything meaningful ? I wasn't so much thinking about the performance benefit, rather the CMPXCHG16B support which IIUC is required for atomics on 128 bit quantities and isn't present in the x86_64 baseline. QEMU already unconditionally adds -mcx16 to its CFLAGS to enable usage of this instruction. I did think there might be some performance benefits too, so it was interesting to see the disappointing results posted elsewhere in this thread. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
