linux-kernel - Re: [PATCH 5/6] x86,fpu: also check fpu_lazy_restore when use_eager

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Date:	Mon, 02 Feb 2015 14:19:35 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	dave.hansen@...ux.intel.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] x86,fpu: also check fpu_lazy_restore when use_eager_fpu

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On 02/02/2015 01:55 PM, Oleg Nesterov wrote:
> On 02/02, riel@...hat.com wrote:
>> 
>> From: Rik van Riel <riel@...hat.com>
>> 
>> With Oleg's patch "x86, fpu: don't abuse FPU in kernel threads
>> if use_eager_fpu()", kernel threads no longer have an FPU state
>> even on systems with use_eager_fpu()
>> 
>> That in turn means that a task may still have its FPU state 
>> loaded in the FPU registers, if the task only got interrupted by 
>> kernel threads from when it went to sleep, to when it woke up 
>> again.
>> 
>> In that case, there is no need to restore the FPU state for this
>> task, since it is still in the registers.
>> 
>> The kernel can simply use the same logic to determine this as is
>> used for !use_eager_fpu() systems.
> 
> Yes, agreed, I was going to do this too.
> 
> And in fact this change make sense even without "don't abuse FPU in
> kernel threads", I think.
> 
> But in theory it depends on another change, "__kernel_fpu_begin()
> should clear fpu_owner_task even if use_eager_fpu()".
> 
> And that series was ignored ;)
> 
> I think this patch is fine.

Ingo,

does the FPU code have a sub-maintainer, or should all the
FPU patches go straight through you?

Would it be better for you if FPU patches came through a git
tree you could just pull?

- -- 
All rights reversed
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