On Wed, Jun 12, 2024 at 11:50:00AM -0400, Ben Cotton wrote: > On Wed, Jun 12, 2024 at 8:41 AM Daniel P. Berrangé <berrange@xxxxxxxxxx> wrote: > > > > The context is that QEMU has recently merged changes upstream that force > > use of the x86-64-v2 baseline for QEMU, in order get more efficient code > > in the TCG emulator. The changes were made in QEMU's global CFLAGS so this > > will affect all usage of QEMU, whether KVM, or TCG, for both VMs and user > > space emulation (the latter used by podman for non-native containers) > > > > IOW, if [when] we rebase Fedora to the next QEMU upstream release, users > > with older x86_64 hardware would likely be unable to run QEMU, from F41 > > onwards, unless some TBD action is taken. > > Could the answer be "we patch the build to not use the changed FLAGS"? > (Perhaps also creating a qemu-zoomzoom package that's the same as the > regular qemu but with the upstream CFLAGS that people who can take > advantage can install instead) It isn't as simple as changing the CFLAGS. QEMU used to check for the CPU feature at startup, set a flag, and then later use that flag to choose different codepaths, but this logic was removed. Avoiding the flag check in hot-paths makes a perf difference. So we would have to revert the whole patch series in Fedora. That's doable today, but I'm not confident carrying a local only revert over time. With 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, report it: https://pagure.io/fedora-infrastructure/new_issue
