linux-kernel - Re: [PATCH 7/8] x86,fpu: use disable_task_lazy_fpu

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Message-ID: <20150217090041.GB9784@pd.tnic>
Date:	Tue, 17 Feb 2015 10:00:41 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	riel@...hat.com
Cc:	oleg@...hat.com, dave.hansen@...ux.intel.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...nel.org,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] x86,fpu: use disable_task_lazy_fpu_restore helper

On Fri, Feb 06, 2015 at 03:02:04PM -0500, riel@...hat.com wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> Replace magic assignments of fpu.last_cpu = ~0 with more explicit
> disable_task_lazy_fpu_restore calls.
> 
> This also fixes the lazy FPU restore disabling in drop_fpu, which
> only really works when !use_eager_fpu().  This is fine for now,
> because fpu_lazy_restore() is only used when !use_eager_fpu()
> currently, but we may want to expand that.

Sorry, I can't follow here. The only non-trivial change below is in
arch_dup_task_struct(). Please clarify.

[ leaving in the rest for context ]

> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
> ---
>  arch/x86/include/asm/fpu-internal.h | 4 ++--
>  arch/x86/kernel/i387.c              | 2 +-
>  arch/x86/kernel/process.c           | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
> index 04063751ac80..06af286593d7 100644
> --- a/arch/x86/include/asm/fpu-internal.h
> +++ b/arch/x86/include/asm/fpu-internal.h
> @@ -440,7 +440,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
>  					     new->thread.fpu_counter > 5);
>  	if (__thread_has_fpu(old)) {
>  		if (!__save_init_fpu(old))
> -			old->thread.fpu.last_cpu = ~0;
> +			task_disable_lazy_fpu_restore(old);
>  		else
>  			old->thread.fpu.last_cpu = cpu;
>  		old->thread.fpu.has_fpu = 0;	/* But leave fpu_owner_task! */
> @@ -454,7 +454,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
>  			stts();
>  	} else {
>  		old->thread.fpu_counter = 0;
> -		old->thread.fpu.last_cpu = ~0;
> +		task_disable_lazy_fpu_restore(old);
>  		if (fpu.preload) {
>  			new->thread.fpu_counter++;
>  			if (!use_eager_fpu() && fpu_lazy_restore(new, cpu))
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index 8e070a6c30e5..8416b5f85806 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -250,7 +250,7 @@ int init_fpu(struct task_struct *tsk)
>  	if (tsk_used_math(tsk)) {
>  		if (cpu_has_fpu && tsk == current)
>  			unlazy_fpu(tsk);
> -		tsk->thread.fpu.last_cpu = ~0;
> +		task_disable_lazy_fpu_restore(tsk);
>  		return 0;
>  	}
>  
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index dd9a069a5ec5..83480373a642 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -68,8 +68,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
>  
>  	dst->thread.fpu_counter = 0;
>  	dst->thread.fpu.has_fpu = 0;
> -	dst->thread.fpu.last_cpu = ~0;
>  	dst->thread.fpu.state = NULL;
> +	task_disable_lazy_fpu_restore(dst);
>  	if (tsk_used_math(src)) {
>  		int err = fpu_alloc(&dst->thread.fpu);
>  		if (err)
> -- 
> 1.9.3
> 
> --
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-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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