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x86_64: use immediate constants in __clear_user()

PATCH New Alexey Dobriyan 2 participants 2 messages May 7, 2018 – May 14, 2018 x86

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Alexey Dobriyan

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#0 lore raw

PATCH 1/1 x86_64: use immediate constants in __clear_user()

Save 2 registers. Adding constants should be just as fast as adding registers.

Signed-off-by Alexey Dobriyan <[email protected]>

---

 arch/x86/lib/usercopy_64.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
arch/x86/lib/usercopy_64.c +4 -5
@@ -23,13 +23,13 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
 	asm volatile(
 		"	testq  %[size8],%[size8]\n"
 		"	jz     4f\n"
-		"0:	movq %[zero],(%[dst])\n"
-		"	addq   %[eight],%[dst]\n"
+		"0:	movq $0,(%[dst])\n"
+		"	addq   $8,%[dst]\n"
 		"	decl %%ecx ; jnz   0b\n"
 		"4:	movq  %[size1],%%rcx\n"
 		"	testl %%ecx,%%ecx\n"
 		"	jz     2f\n"
-		"1:	movb   %b[zero],(%[dst])\n"
+		"1:	movb   $0,(%[dst])\n"
 		"	incq   %[dst]\n"
 		"	decl %%ecx ; jnz  1b\n"
 		"2:\n"

@@ -40,8 +40,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
 		_ASM_EXTABLE(0b,3b)
 		_ASM_EXTABLE(1b,2b)
 		: [size8] "=&c"(size), [dst] "=&D" (__d0)
-		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),
-		  [zero] "r" (0UL), [eight] "r" (8UL));
+		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
 	clac();
 	return size;
 }
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#1 lore raw

[tip:x86/asm] x86/asm/64: Micro-optimize __clear_user() - Use immediate constants

x86/asm/64: Micro-optimize __clear_user() - Use immediate constants
Commit-ID:  1153933703d927b3d4874c0bc801de32b1b58be9
Gitweb:     https://git.kernel.org/tip/1153933703d927b3d4874c0bc801de32b1b58be9
Author:     Alexey Dobriyan <[email protected]>
AuthorDate: Tue, 8 May 2018 00:39:37 +0300
Committer:  Ingo Molnar <[email protected]>
CommitDate: Mon, 14 May 2018 11:38:51 +0200

x86/asm/64: Micro-optimize __clear_user() - Use immediate constants

Save two registers. Adding constants should be just as fast as adding registers.

Signed-off-by Alexey Dobriyan <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Link http://lkml.kernel.org/r/20180507213937.GB32406@avx2 open here
Signed-off-by Ingo Molnar <[email protected]>
---
 arch/x86/lib/usercopy_64.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
arch/x86/lib/usercopy_64.c +4 -5
index 75d3776123cc..a624dcc4de10 100644
@@ -23,13 +23,13 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
 	asm volatile(
 		"	testq  %[size8],%[size8]\n"
 		"	jz     4f\n"
-		"0:	movq %[zero],(%[dst])\n"
-		"	addq   %[eight],%[dst]\n"
+		"0:	movq $0,(%[dst])\n"
+		"	addq   $8,%[dst]\n"
 		"	decl %%ecx ; jnz   0b\n"
 		"4:	movq  %[size1],%%rcx\n"
 		"	testl %%ecx,%%ecx\n"
 		"	jz     2f\n"
-		"1:	movb   %b[zero],(%[dst])\n"
+		"1:	movb   $0,(%[dst])\n"
 		"	incq   %[dst]\n"
 		"	decl %%ecx ; jnz  1b\n"
 		"2:\n"

@@ -40,8 +40,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
 		_ASM_EXTABLE(0b,3b)
 		_ASM_EXTABLE(1b,2b)
 		: [size8] "=&c"(size), [dst] "=&D" (__d0)
-		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),
-		  [zero] "r" (0UL), [eight] "r" (8UL));
+		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
 	clac();
 	return size;
 }