linux-kernel - Re: [RFC PATCH 03/11] x86,fpu: move __thread_fpu

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Message-ID: <54B549E2.3040303@redhat.com>
Date:	Tue, 13 Jan 2015 11:37:54 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, bp@...e.de, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 03/11] x86,fpu: move __thread_fpu_begin to when the
 task has the fpu

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On 01/13/2015 10:24 AM, Oleg Nesterov wrote:
> On 01/11, riel@...hat.com wrote:
>> 
>> --- a/arch/x86/include/asm/fpu-internal.h +++
>> b/arch/x86/include/asm/fpu-internal.h @@ -420,7 +420,6 @@ static
>> inline void switch_fpu_prepare(struct task_struct *old, struct
>> task_struc if (preload) { new->thread.fpu_counter++; 
>> set_thread_flag(TIF_LOAD_FPU); -			__thread_set_has_fpu(new); 
>> prefetch(new->thread.fpu.state); } else if (!use_eager_fpu()) 
>> stts(); @@ -436,7 +435,6 @@ static inline void
>> switch_fpu_prepare(struct task_struct *old, struct task_struc 
>> prefetch(new->thread.fpu.state); set_thread_flag(TIF_LOAD_FPU); 
>> } -			__thread_fpu_begin(new); } /* else: CR0.TS is still set
>> from a previous FPU switch */ } @@ -451,6 +449,7 @@ static inline
>> void switch_fpu_prepare(struct task_struct *old, struct
>> task_struc static inline void switch_fpu_finish(struct
>> task_struct *new) { if (test_and_clear_thread_flag(TIF_LOAD_FPU))
>> { +		__thread_fpu_begin(new); if
>> (unlikely(restore_fpu_checking(new))) drop_init_fpu(new); }
> 
> Then perhaps it makes sense to move fpu_lazy_restore() to
> fpu_finish() too ?

I do that later in the series.  I would like to keep that in a
separate changeset, for bisecting reasons.

> Either way, afaics we do not need use_eager_fpu() before
> fpu_lazy_restore(), and this reminds me that every use_eager_fpu()
> check in switch_fpu_prepare() looks confusing.

Agreed. The patch that moves fpu_lazy_restore() into
switch_fpu_finish() also removes the use_eager_fpu()
condition for that.

Another reason for it to be by itself in its own
changeset :)

- -- 
All rights reversed
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