Disabling speculative execution mitigations

[O'Connor, Daniel]

Hi,
I am trying to track down a performance drop with the ASPEED xorg video driver between FreeBSD 11 and 12 (I'm not expecting miracles from it but it was basically unusable..)

I wondered if some of the speculative execution mitigations could be causing the problem so I did some digging and found these..

vm.pmap.pti="0"        # Disable page table isolation
hw.ibrs_disable="1"    # Disable Indirect Branch Restricted Speculation
hw.mds_disable="0"     # Disable Microarchitectural Data Sampling flush
hw.vmm.vmx="1"         # Don't flush RSB on vmexit (presumably only affects bhyve etc)
hw.lazy_fpu_switch="1" # Lazily flush FPU

Does anyone know of any others?

I have 2 systems with the same motherboard (Supermicro X11SSH-F), one is older and runs FreeBSD 11 (and had an older BIOS_ and the newer runs FreeBSD 12.

FWIW on FreeBSD 11 the performance (measured by a subset of x11perf benchmarks) went down 40% after updating to the latest BIOS (2.2a). Unfortunately on FreeBSD 12 rolling back to the original BIOS (2.2) did not improve performance.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum