On Wed, Jun 12, 2024 at 1:04 PM Daniel P. Berrangé <[email protected]> wrote: > > On Wed, Jun 12, 2024 at 01:55:20PM +0300, Alexander Monakov wrote: > > Hello, > > > > I'm sending straightforward reverts to recent patches that bumped minimum > > required x86 instruction set to SSE4.2. The older chips did not stop > > working, > > and people still test and use new software on older hardware: > > https://sourceware.org/bugzilla/show_bug.cgi?id=31867 > > > > Considering the very minor gains from the baseline raise, I'm honestly not > > sure why it happened. It seems better to let distributions handle that. > > Indeed distros are opinionated about the x86_64 baseline they want > to target. > > While RHEL-9 switched to a x86_64-v2 baseline, Fedora has repeatedly > rejected the idea of moving to an x86_64-v2 baseline, wanting to retain > full backwards compat. So this assumption in QEMU is preventing the > distros from satisfying their chosen build target goals.
I didn't do this because of RHEL9, I did it because it's silly that QEMU cannot use POPCNT and has to waste 2% of the L1 d-cache to compute the x86 parity flag (and POPCNT was introduced at the same time as SSE4.2). Intel x86_64-v2 processors have been around for about 15 years, AMD for a little less (2011). I'd rather hear from users about the usecases for running QEMU on such old processors before reverting, as this does not get in the way of booting/installing distros on old machines. Unless QEMU is run from within the installation media, which it isn't, requiring a particular processor family does not prevent Fedora from being installable on pre-v2 processors. Paolo
