linux-kernel - [patch 13/13] syslets: x86: optimized sys_umem

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Date:	Wed, 21 Feb 2007 22:16:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [patch 13/13] syslets: x86: optimized sys_umem_add()

From: Ingo Molnar <mingo@...e.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@...e.hu>
Signed-off-by: Arjan van de Ven <arjan@...ux.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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