linux-kernel - Re: [PATCH 1/1] SGI UV: TLB shootdown using broadcast assist unit

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Date:	Wed, 04 Jun 2008 14:44:59 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Cliff Wickman <cpw@....com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/1] SGI UV: TLB shootdown using broadcast assist unit

Cliff Wickman wrote:
> Signed-off-by: Cliff Wickman <cpw@....com>
> ---
>  arch/x86/kernel/Makefile    |    2 
>  arch/x86/kernel/entry_64.S  |    4 
>  arch/x86/kernel/tlb_64.c    |    5 
>  arch/x86/kernel/tlb_uv.c    |  785 ++++++++++++++++++++++++++++++++++++++++++++
>  include/asm-x86/atomic_64.h |   30 +
>   

The atomic_64.h changes should be a separate patch.

> Index: 080602.ingo/include/asm-x86/atomic_64.h
> ===================================================================
> --- 080602.ingo.orig/include/asm-x86/atomic_64.h
> +++ 080602.ingo/include/asm-x86/atomic_64.h
> @@ -425,6 +425,36 @@ static inline int atomic64_add_unless(at
>  	return c != (u);
>  }
>  
> +/**
> + * atomic_inc_short - increment of a short integer
> + * @v: pointer to type int
> + *
> + * Atomically adds 1 to @v
> + * Returns the new value of @u
> + */
> +static inline short int atomic_inc_short(short int *v)
> +{
> +	asm volatile("movw $1, %%cx; lock; xaddw %%cx, %0\n"
> +		: "+m" (*v) : : "cx");
> +		/* clobbers counter register cx */
> +	return *v;
> +}
>   
Why?  Why not just:

	asm("lock add $1, %0" : "+m" (*v));

Does xaddw buy anything here?

> +
> +/**
> + * atomic_or_long - OR of two long integers
> + * @v1: pointer to type unsigned long
> + * @v2: pointer to type unsigned long
> + *
> + * Atomically ORs @v1 and @v2
> + * Returns the result of the OR
> + */
> +static inline void atomic_or_long(unsigned long *v1, unsigned long v2)
> +{
> +	asm volatile("movq %1, %%rax; lock; orq %%rax, %0\n"
> +		: "+m" (*v1) : "g" (v2): "rax");
> +		/* clobbers accumulator register ax */
>   

How about:

	asm("lock or %1, %0" : "+m" (*v1), "r" (v2));

No need to force %rax, is there?


    J
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