Re: [PATCH 2/9] x86/fpu: Hard-disable lazy fpu mode

From: Paolo Bonzini
Date: Wed Oct 05 2016 - 03:14:33 EST

On 05/10/2016 02:34, riel@xxxxxxxxxx wrote:
> From: Andy Lutomirski <luto@xxxxxxxxxx>
> Since commit 58122bf1d856 ("x86/fpu: Default eagerfpu=on on all
> CPUs") in Linux 4.6, eager FPU mode has been the default on all x86
> systems, and no one has reported any regressions.
> This patch removes the ability to enable lazy mode: use_eager_fpu()
> becomes "return true" and all of the FPU mode selection machinery is
> removed.

I haven't quite followed up on my promise to benchmark lazy vs. eager
FPU, but I probably should do that now...

I see two possible issues with this. First, AMD as far as I know does
not have XSAVEOPT. Second, when using virtualization, depending on how
you configure your cluster it's enough to have one pre-SandyBridge Intel
machine to force no XSAVE on all machines.