Re: [patch 2.6.17-rc5 1/2] i386 memcpy: use as few moves as possible for I/O

[Chuck Ebbert]

In-Reply-To: <447D1094.20409@xxxxxxxxx>

On Tue, 30 May 2006 20:42:12 -0700, H. Peter Anvin wrote:

> I was thinking some more about that, and I suspect the "right" way to do 
> this looks something like the attached code.  Note that it assymetric, 
> and that it's probably too long to inline.
> 
> I haven't tested this yet, and I probably won't have time to do so this 
> evening.

There were some small problems, but I think I fixed them:


/*
 * arch/i386/lib/memcpy_io.S
 *
 * The most general form of memory copy to/from I/O space, used for
 * devices which can handle arbitrary transactions with appropriate
 * handling of byte enables.  The goal is to produce the minimum
 * number of naturally aligned transactions on the bus.
 */
	
#include <linux/config.h>
#include <linux/linkage.h>
	
.macro	build_memcpy_io_fn fn_name,align_reg

	.globl	\fn_name
	.type	\fn_name, @function
	
	ALIGN
\fn_name:

	ebp_space=0
#ifdef CONFIG_FRAME_POINTER
	pushl	%ebp
	movl	%esp,%ebp
	ebp_space=4
#endif

	pushl	%edi
	pushl	%esi
	
#ifdef CONFIG_REGPARM
	movl	%eax, %edi
	movl	%edx, %esi
#else
	movl	12+ebp_space(%esp), %edi
	movl	20+ebp_space(%esp), %ecx
	movl	16+ebp_space(%esp), %esi
#endif

	jecxz	1f
	
	testl	$1, \align_reg
	jz	2f
	movsb
	decl	%ecx
2:
	cmpl	$2, %ecx
	jb	3f
	testl	$2, \align_reg
	jz	4f
	movsw
	decl	%ecx
	decl	%ecx
4:
	movl	%ecx, %edx
	shrl	$2, %ecx
	jz	5f
	rep ; movsl
5:
	movl	%edx, %ecx
	testb	$2, %cl
	jz	3f
	movsw
3:
	testb	$1, %cl
	jz	1f
	movsb
1:
	pop	%esi
	pop	%edi

#ifdef CONFIG_FRAME_POINTER
	leave
#endif

	ret

	.size	\fn_name, .-\fn_name

.endm

	build_memcpy_io_fn fn_name=memcpy_fromio,align_reg=%esi
	build_memcpy_io_fn fn_name=memcpy_toio,align_reg=%edi
-- 
Chuck
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