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Re: [Xen-devel] [PATCH v1] x86/spec-ctrl: Remove EAGER_FPU when PV/HVM is disabled.
- To: Jin Nan Wang <jnwang@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 5 Aug 2019 10:04:09 +0100
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 05 Aug 2019 09:04:28 +0000
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On 05/08/2019 09:54, Jin Nan Wang wrote:
> In commit ac3f9a72141a48d40fabfff561d5a7dc0e1b810d:
> For one, "no-xen" should not imply "no-eager-fpu", as "eager FPU" mode
> is to guard guests, not Xen itself, which is also expressed so by
> print_details().
>
> So when spec-ctrl=pv=off,hvm=off; EAGER_FPU shouldn't be display in lines:
> Current[Wrong]:
> (XEN) Support for HVM VMs: EAGER_FPU MD_CLEAR
> (XEN) Support for PV VMs: EAGER_FPU MD_CLEAR
>
> expectation:
> (XEN) Support for HVM VMs: MD_CLEAR
> (XEN) Support for PV VMs: MD_CLEAR
Eager FPU is a performance win across the board. It will become an even
bigger performance win when we follow in Linux's footsteps and remove
the eager option, and associated logic.
I don't see any value in turning it off for speculation related reasons.
~Andrew
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