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Subject[patch 13/13] syslets: x86: optimized sys_umem_add()
From: Ingo Molnar <mingo@elte.hu>

provide an optimized assembly version of sys_umem_add().
It is about 2 times faster than the C version.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
arch/i386/lib/getuser.S | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

Index: linux/arch/i386/lib/getuser.S
===================================================================
--- linux.orig/arch/i386/lib/getuser.S
+++ linux/arch/i386/lib/getuser.S
@@ -11,6 +11,33 @@
#include <asm/thread_info.h>

/*
+ * Optimized user-memory arithmetics system-call:
+ */
+
+.text
+.align 4
+.globl sys_umem_add
+sys_umem_add:
+ movl 0x4(%esp), %ecx # uptr
+ movl 0x8(%esp), %edx # inc
+
+ cmpl $__PAGE_OFFSET, %ecx # access_ok(uptr)
+ jae bad_sys_umem_add
+
+1: addl %edx, (%ecx) # *uptr += inc
+2: movl (%ecx), %eax # return *uptr
+ ret
+
+bad_sys_umem_add:
+ movl $-14, %eax
+ ret
+
+.section __ex_table,"a"
+ .long 1b, bad_sys_umem_add
+ .long 2b, bad_sys_umem_add
+.previous
+
+/*
* copy_uatom() - copy a syslet_atom from user-space into kernel-space:
*/

-
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