Re: [PATCH] atomic_inc_return() for i386[1/5] (Re: atomic_inc_return)

[Andrew Morton <akpm@osdl.org>]

kaigai@ak.jp.nec.com (Kaigai Kohei) wrote:
>
> 
> [1/5] atomic_inc_return-linux-2.6.9-rc1.i386.patch
>   This patch implements atomic_inc_return() and so on for i386,
>   and includes runtime check whether CPU is legacy 386.
>   It is same as I posted to LKML and Andi Kleen at '04/09/01.
> 

Can we not use the `alternative instruction' stuff to eliminate the runtime
test?


> 
> diff -rNU4 linux-2.6.9-rc1/include/asm-i386/atomic.h linux-2.6.9-rc1.atomic_inc_return/include/asm-i386/atomic.h
> --- linux-2.6.9-rc1/include/asm-i386/atomic.h	2004-08-24 16:02:24.000000000 +0900
> +++ linux-2.6.9-rc1.atomic_inc_return/include/asm-i386/atomic.h	2004-09-10 10:15:18.000000000 +0900
> @@ -1,8 +1,10 @@
>  #ifndef __ARCH_I386_ATOMIC__
>  #define __ARCH_I386_ATOMIC__
>  
>  #include <linux/config.h>
> +#include <linux/compiler.h>
> +#include <asm/processor.h>
>  
>  /*
>   * Atomic operations that C can't guarantee us.  Useful for
>   * resource counting etc..
> @@ -175,8 +177,48 @@
>  		:"ir" (i), "m" (v->counter) : "memory");
>  	return c;
>  }
>  
> +/**
> + * atomic_add_return - add and return
> + * @v: pointer of type atomic_t
> + * @i: integer value to add
> + *
> + * Atomically adds @i to @v and returns @i + @v
> + */
> +static __inline__ int atomic_add_return(int i, atomic_t *v)
> +{
> +	int __i;
> +#ifdef CONFIG_M386
> +	if(unlikely(boot_cpu_data.x86==3))
> +		goto no_xadd;
> +#endif
> +	/* Modern 486+ processor */
> +	__i = i;
> +	__asm__ __volatile__(
> +		LOCK "xaddl %0, %1;"
> +		:"=r"(i)
> +		:"m"(v->counter), "0"(i));
> +	return i + __i;
> +
> +#ifdef CONFIG_M386
> +no_xadd: /* Legacy 386 processor */
> +	local_irq_disable();
> +	__i = atomic_read(v);
> +	atomic_set(v, i + __i);
> +	local_irq_enable();
> +	return i + __i;
> +#endif
> +}
> +
> +static __inline__ int atomic_sub_return(int i, atomic_t *v)
> +{
> +	return atomic_add_return(-i,v);
> +}
> +
> +#define atomic_inc_return(v)  (atomic_add_return(1,v))
> +#define atomic_dec_return(v)  (atomic_sub_return(1,v))
> +
>  /* These are x86-specific, used by some header files */
>  #define atomic_clear_mask(mask, addr) \
>  __asm__ __volatile__(LOCK "andl %0,%1" \
>  : : "r" (~(mask)),"m" (*addr) : "memory")