FSGSBASE Testing Is Encouraged Ahead Of Linux 5.9

[Space Heater]

FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors. I had to remove FSGSBASE patches from Zen Kernel after a report that a 3950x user was getting stalls and freezes after the patches were added: https://github.com/zen-kernel/zen-kernel/issues/172

I saw in the bug report another user reported system freezes with qemu/kvm virtual machines and FSGSBASE.

On 5.8-rc2 with FSGSBASE patches, I've run a Windows vm via qemu/kvm for over 12 hours now and so far I've experienced no hangs or oops messages.

[V1tol]

Another one stupid question - if I use "mitigations=off" will performance change at all with this patch?

[ezst036]

Thank you.

[Space Heater]

what would be the earliest processor family that might benefit from this?

It would appear that 15h and newer support FSGSBASE, so that is Bulldozer and newer. I'm not sure if 16h (Jaguar/Puma) support it though.

Source: AMD's BIOS and Kernel Developer’s Guide. (page 32, under "Architectural changes")

[ezst036]

Is it true this also speeds up AMD CPUs?

For anybody who knows, what would be the earliest processor family that might benefit from this? Bulldozer? K10h?(phenom II, etc)

[Space Heater]

FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors.

Given that the bug report was posted before the current revision of the FSGSBASE patches came out, I'd suggest checking again to see if the problem still persists (and on an otherwise mainline kernel).

[damentz]

FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors. I had to remove FSGSBASE patches from Zen Kernel after a report that a 3950x user was getting stalls and freezes after the patches were added: https://github.com/zen-kernel/zen-kernel/issues/172

[_Alex_]

In the geometric mean, AMD got more performance (+7.3% vs intel 6.1%): https://openbenchmarking.org/embed.p...ha=432aff7&p=2

[Space Heater]

Is it true this also speeds up AMD CPUs?

Yes, but the improvement isn't likely to be as noticeable, as context switches are currently less expensive on AMD systems.

You can look at Michael's earlier benchmarks.

[milkylainen]

Just the sheer engineering keeping the old turd afloat...

I remember when cpuinfo features was a oneliner. Now it's like a novel...
... And f00f/fdiv was all you needed to know before Intel screwed everything up...