Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=15ae02baf025750cd79ef3929c28f7083a088bd2
Commit: 15ae02baf025750cd79ef3929c28f7083a088bd2
Parent: f63fd7e299ee13da071ecfce2b90b58c5e1562b1
Author: Eric Dumazet <[EMAIL PROTECTED]>
AuthorDate: Wed Feb 6 01:37:49 2008 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 10:41:08 2008 -0800
lib/extable.c: remove an expensive integer divide in search_extable()
Actual code let compiler generates idiv instruction on x86.
Using a right shift is OK here and readable as well.
Before patch
10: 57 push %edi
11: 56 push %esi
12: 89 d6 mov %edx,%esi
14: 53 push %ebx
15: 89 c3 mov %eax,%ebx
17: eb 22 jmp 3b <search_extable+0x2b>
19: 89 f0 mov %esi,%eax
1b: ba 02 00 00 00 mov $0x2,%edx
20: 29 d8 sub %ebx,%eax
22: 89 d7 mov %edx,%edi
24: c1 f8 03 sar $0x3,%eax
27: 99 cltd
28: f7 ff idiv %edi
2a: 8d 04 c3 lea (%ebx,%eax,8),%eax
2d: 39 08 cmp %ecx,(%eax)
...
After patch
00000010 <search_extable>:
10: 53 push %ebx
11: 89 c3 mov %eax,%ebx
13: eb 18 jmp 2d <search_extable+0x1d>
15: 89 d0 mov %edx,%eax
17: 29 d8 sub %ebx,%eax
19: c1 f8 04 sar $0x4,%eax
1c: 8d 04 c3 lea (%ebx,%eax,8),%eax
1f: 39 08 cmp %ecx,(%eax)
...
Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
lib/extable.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/lib/extable.c b/lib/extable.c
index 463f456..179c087 100644
--- a/lib/extable.c
+++ b/lib/extable.c
@@ -57,10 +57,10 @@ search_extable(const struct exception_table_entry *first,
while (first <= last) {
const struct exception_table_entry *mid;
- mid = (last - first) / 2 + first;
+ mid = ((last - first) >> 1) + first;
/*
- * careful, the distance between entries can be
- * larger than 2GB:
+ * careful, the distance between value and insn
+ * can be larger than MAX_LONG:
*/
if (mid->insn < value)
first = mid + 1;
-
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