diff options
| author | Eric Dumazet <dada1@cosmosbay.com> | 2008-02-06 01:37:49 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-06 10:41:08 -0800 |
| commit | 15ae02baf025750cd79ef3929c28f7083a088bd2 (patch) | |
| tree | 9c79b44e5ec865ff62a451bb6e4882d3f4d5b060 /lib/extable.c | |
| parent | f63fd7e299ee13da071ecfce2b90b58c5e1562b1 (diff) | |
| download | lwn-15ae02baf025750cd79ef3929c28f7083a088bd2.tar.gz lwn-15ae02baf025750cd79ef3929c28f7083a088bd2.zip | |
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 <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/extable.c')
| -rw-r--r-- | lib/extable.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/lib/extable.c b/lib/extable.c index 463f4560f16d..179c08745595 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; |