Re: Intel P6 vs P7 system call performance

[Petr Vandrovec]

On Sun, Dec 22, 2002 at 09:03:44PM -0800, Linus Torvalds wrote:
> 
> How does the attached patch work for people? I've verified that
> single-stepping works, and I've also verified that it does improve
> performance for simple system calls. Everything looks quite simple.

> ===== arch/i386/kernel/sysenter.c 1.4 vs edited =====
> --- 1.4/arch/i386/kernel/sysenter.c	Sat Dec 21 16:02:02 2002
> +++ edited/arch/i386/kernel/sysenter.c	Sun Dec 22 20:17:28 2002
> @@ -54,19 +54,18 @@
>  		0xc3			/* ret */
>  	};
>  	static const char sysent[] = {
> -		0x9c,			/* pushf */
>  		0x51,			/* push %ecx */
>  		0x52,			/* push %edx */
>  		0x55,			/* push %ebp */
>  		0x89, 0xe5,		/* movl %esp,%ebp */
>  		0x0f, 0x34,		/* sysenter */
> +		0x00,			/* align return point */
>  	/* System call restart point is here! (SYSENTER_RETURN - 2) */
>  		0xeb, 0xfa,		/* jmp to "movl %esp,%ebp" */

Hi Linus,

Jump instruction should be 0xeb, 0xf9, with 0xeb, 0xfa it jumps into 
the middle of movl %esp,%ebp because of added alignment.

Maybe glibc tests needs also something to check restarted syscall...
					Thanks,
						Petr Vandrovec
						[e-mail]

--- linux/arch/i386/kernel/sysenter.c.orig	2002-12-24 00:23:41.000000000 +0100
+++ linux/arch/i386/kernel/sysenter.c	2002-12-24 00:23:50.000000000 +0100
@@ -61,7 +61,7 @@
 		0x0f, 0x34,		/* sysenter */
 		0x00,			/* align return point */
 	/* System call restart point is here! (SYSENTER_RETURN - 2) */
-		0xeb, 0xfa,		/* jmp to "movl %esp,%ebp" */
+		0xeb, 0xf9,		/* jmp to "movl %esp,%ebp" */
 	/* System call normal return point is here! (SYSENTER_RETURN in entry.S) */
 		0x5d,			/* pop %ebp */
 		0x5a,			/* pop %edx */