diff options
| author | Alexey Dobriyan <adobriyan@gmail.com> | 2019-07-16 16:27:12 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-16 19:23:22 -0700 |
| commit | 4c6080cd6f8baad9f7faa3deac9a90e59726b119 (patch) | |
| tree | a5c524c477de164edc2c2c51029f1e7202af03b8 | |
| parent | 49662503e8e4df9db29bfc354112a9a6312d7a25 (diff) | |
lib/list: tweak LIST_POISON2 for better code generation on x86_64
list_del() poisoning can generate 2 64-bit immediate loads but it also can
generate one 64-bit immediate load and an addition:
48 b8 00 01 00 00 00 00 ad de movabs rax,0xdead000000000100
48 89 47 58 mov QWORD PTR [rdi+0x58],rax
48 05 00 01 00 00 <=====> add rax,0x100
48 89 47 60 mov QWORD PTR [rdi+0x60],rax
However on x86_64 not all constants are equal: those within [-128, 127]
range can be added with shorter "add r64, imm32" instruction:
48 b8 00 01 00 00 00 00 ad de movabs rax,0xdead000000000100
48 89 47 58 mov QWORD PTR [rdi+0x58],rax
48 83 c0 22 <======> add rax,0x22
48 89 47 60 mov QWORD PTR [rdi+0x60],rax
Patch saves 2 bytes per some LIST_POISON2 usage.
(Slightly disappointing) space savings on F29 x86_64 config:
add/remove: 0/0 grow/shrink: 0/2164 up/down: 0/-5184 (-5184)
Function old new delta
zstd_get_workspace 548 546 -2
...
mlx4_delete_all_resources_for_slave 4826 4804 -22
Total: Before=83304131, After=83298947, chg -0.01%
New constants are:
0xdead000000000100
0xdead000000000122
Note: LIST_POISON1 can't be changed to ...11 because something in page
allocator requires low bit unset.
Link: http://lkml.kernel.org/r/20190513191502.GA8492@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | include/linux/poison.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/poison.h b/include/linux/poison.h index d6d980a681c7..df34330b4e34 100644 --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -21,7 +21,7 @@ * non-initialized list entries. */ #define LIST_POISON1 ((void *) 0x100 + POISON_POINTER_DELTA) -#define LIST_POISON2 ((void *) 0x200 + POISON_POINTER_DELTA) +#define LIST_POISON2 ((void *) 0x122 + POISON_POINTER_DELTA) /********** include/linux/timer.h **********/ /* |