On Fri, Feb 09, 2018 at 08:11:12PM +0100, Joerg Roedel wrote: > On Fri, Feb 09, 2018 at 05:47:43PM +0000, Andy Lutomirski wrote: > > One thing worth noting is that performance of this whole series is > > going to be abysmal due to the complete lack of 32-bit PCID. Maybe > > any kernel built with this option set that runs on a CPU that has the > > PCID bit set in CPUID should print a big fat warning like "WARNING: > > you are using 32-bit PTI on a 64-bit PCID-capable CPU. Your > > performance will increase dramatically if you switch to a 64-bit > > kernel." > > Thanks for your review. I can add this warning, but I just hope that not > a lot of people will actually see it :)
Alas, we got some data: https://popcon.debian.org/ says 20% of x86 users have i386 as their main ABI (current; people with popcon installed). Of those, 80% use 32-bit kernels: i686 881, x86_64 229, i586 14 (uname -m included in bug reports; data for 2016) -- and bug reporters tend to have more clue than the average user. There's no way so many folks still use pre-2004 computers. Thus, if you could include that big fat warning, distro developers would be thankful. Make it show fiery letters if you can. Preferably, we'd want a huge mallet reach out of the screen and bonk the user on the head, but with that impossible, a scary message would help. Let them use 32-bit userland, but if someone runs such a kernel on a modern machine, some kind of verbal abuse is warranted. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢰⠒⠀⣿⡁ Vat kind uf sufficiently advanced technology iz dis!? ⢿⡄⠘⠷⠚⠋⠀ -- Genghis Ht'rok'din ⠈⠳⣄⠀⠀⠀⠀
