On 11/03/2016 22:33, David Matlack wrote: > > Is this better than just always keeping the host's XCR0 loaded outside > > if the KVM interrupts-disabled region? > > Probably not. AFAICT KVM does not rely on it being loaded outside that > region. xsetbv isn't insanely expensive, is it? Maybe to minimize the > time spent with interrupts disabled it was put outside. > > I do like that your solution would be contained to KVM.
I agree with Andy. We do want a fix for recent kernels because of the !eager_fpu case that Guangrong mentioned. Paolo ps: while Andy is planning to kill lazy FPU, I want to benchmark it with KVM... Remember that with a single pre-xsave host in your cluster, your virt management might happily default your VMs to a Westmere or Nehalem CPU model. GCC might be a pretty good testbench for this (e.g. a kernel compile with very high make -j), because outside of the lexer (which plays SIMD games) it never uses the FPU.
