Subject: Re: [PATCH 2/9] x86/fpu: Hard-disable lazy fpu mode
To: riel@redhat.com, linux-kernel@vger.kernel.org
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Cc: dave.hansen@linux.intel.com, x86@kernel.org, tglx@linutronix.de,
        mingo@redhat.com, luto@kernel.org, pa@zytor.com, bp@suse.de
From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 5 Oct 2016 09:14:21 +0200
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On 05/10/2016 02:34, riel@redhat.com wrote:
> From: Andy Lutomirski <luto@kernel.org>
> 
> 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.

Thanks,

Paolo