Re: [PATCH] x86/fpu: Revert earlier patch of Disable AVX when eagerfpu is off

[H. Peter Anvin]

On 03/09/2016 04:46 AM, Ingo Molnar wrote:
> 
> * Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
> 
>> AVX was mistakenly believed to be dependent on eagerfpu switch.
>> This turns out to be false. The earlier patch should be reverted.
>>
>> Original patch:
>>     http://git.kernel.org/tip/394db20ca240741a08d472173db13d6f6a6e5a28
> 
> So the original patch had a whole host of explanations of why that change is 
> correct. This revert should explain where that argumentation was wrong.
> 
> Also note that eagerfpu=off is on the way out, on v4.6 we'll switch all CPUs to 
> eagerfpu:
> 
>   58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs
> 
> and in the not so distant future, if everything goes fine with the eager mode, I'd 
> like to drop the lazy FPU context switching code altogether - which will simplify 
> a lot of code. At that point the 'eagerfpu' boot option will go away as well.
> 

Last I heard the only use case which was seeing trouble with eagerfpu
was KVM during service of I/O events.  Might be worth checking into...

	-hpa