linux-kernel - Re: [PATCH 6/6] x86,fpu: remove redundant increments of fpu

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Date:	Mon, 2 Feb 2015 19:34:18 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	riel@...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 6/6] x86,fpu: remove redundant increments of fpu_counter

On 02/02, riel@...hat.com wrote:
>
> From: Rik van Riel <riel@...hat.com>
>
> fpu.preload only gets set if new->thread.fpu_counter is already
> larger than 5. Incrementing it further does absolutely nothing.
> Remove those lines.

I _think_ that we increment it further on purpose. Note that fpu_counter
is "char", so it seems that we want no more than 256 automatic preloads.

So I am not sure about this change. At least the changelog doesn't look
right.

Oleg.

> --- a/arch/x86/include/asm/fpu-internal.h
> +++ b/arch/x86/include/asm/fpu-internal.h
> @@ -447,7 +447,6 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
>  
>  		/* Don't change CR0.TS if we just switch! */
>  		if (fpu.preload) {
> -			new->thread.fpu_counter++;
>  			__thread_set_has_fpu(new);
>  			prefetch(new->thread.fpu.state);
>  		} else if (!use_eager_fpu())
> @@ -456,7 +455,6 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
>  		old->thread.fpu_counter = 0;
>  		task_disable_lazy_fpu_restore(old);
>  		if (fpu.preload) {
> -			new->thread.fpu_counter++;
>  			if (fpu_lazy_restore(new, cpu))
>  				fpu.preload = 0;
>  			else
> -- 
> 1.9.3
> 

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