linux-kernel - Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs

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Date:	Mon, 23 Feb 2015 07:51:04 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Borislav Petkov <bp@...en8.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Ingo Molnar <mingo@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs

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On 02/23/2015 12:22 AM, Andy Lutomirski wrote:
> On Sun, Feb 22, 2015 at 5:45 PM, Rik van Riel <riel@...hat.com>
> wrote:

>> One implication of this is that in kernel mode, we can no longer
>> just assume that the user space FPU state is always loaded, and
>> we need to check for that (like the lazy FPU code does today).  I
>> would really like to keep that code around, for obvious reasons
>> :)
> 
> I like that stuff, except for the fact that it still has code that 
> depends on whether we're in eager or lazy mode, even though eager
> is a little less eager with your patches.  Ideally I'd like to see
> your patches applied *and* lazy mode removed.

The latest version of my code (which I should forward-port
again to the latest tip bits) simplifies things a lot.

It moves all new task handling to switch_fpu_finished(),
which is called from do_notify_resume().

At that point we either load the FPU context, or we
set CR0.TS.

- -- 
All rights reversed
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