Date: Fri, 6 Dec 2019 15:51:04 +1030 From: "O'Connor, Daniel" <darius@dons.net.au> To: freebsd-stable <freebsd-stable@freebsd.org> Subject: Disabling speculative execution mitigations Message-ID: <C19DE24E-22CB-4E55-95CE-0A07FC8A23F5@dons.net.au>
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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=3D"0" # Disable page table isolation hw.ibrs_disable=3D"1" # Disable Indirect Branch Restricted = Speculation hw.mds_disable=3D"0" # Disable Microarchitectural Data Sampling = flush hw.vmm.vmx=3D"1" # Don't flush RSB on vmexit (presumably only = affects bhyve etc) hw.lazy_fpu_switch=3D"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
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