Commit 15ae02baf025750cd79ef3929c28f7083a088bd2
Committed by
Linus Torvalds
1 parent
f63fd7e299
Exists in
master
and in
4 other branches
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>
Showing 1 changed file with 3 additions and 3 deletions Side-by-side Diff
lib/extable.c
... | ... | @@ -57,10 +57,10 @@ |
57 | 57 | while (first <= last) { |
58 | 58 | const struct exception_table_entry *mid; |
59 | 59 | |
60 | - mid = (last - first) / 2 + first; | |
60 | + mid = ((last - first) >> 1) + first; | |
61 | 61 | /* |
62 | - * careful, the distance between entries can be | |
63 | - * larger than 2GB: | |
62 | + * careful, the distance between value and insn | |
63 | + * can be larger than MAX_LONG: | |
64 | 64 | */ |
65 | 65 | if (mid->insn < value) |
66 | 66 | first = mid + 1; |