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| author | Christophe Leroy <christophe.leroy@csgroup.eu> | 2020-12-15 20:42:45 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-12-15 22:46:15 -0800 |
| commit | 0a571b085ff6dadf946b248133533d3ba68f6e31 (patch) | |
| tree | 5c1578cce2e0561b857c36fbefb265796c8b6b56 /include/asm-generic/getorder.h | |
| parent | a9389683fafcd4b6f7dcef62f9f05d436a12cfb5 (diff) | |
| download | lwn-0a571b085ff6dadf946b248133533d3ba68f6e31.tar.gz lwn-0a571b085ff6dadf946b248133533d3ba68f6e31.zip | |
asm-generic: force inlining of get_order() to work around gcc10 poor decision
When building mpc885_ads_defconfig with gcc 10.1,
the function get_order() appears 50 times in vmlinux:
[linux]# ppc-linux-objdump -x vmlinux | grep get_order | wc -l
50
[linux]# size vmlinux
text data bss dec hex filename
3842620 675624 135160 4653404 47015c vmlinux
In the old days, marking a function 'static inline' was forcing GCC to
inline, but since commit ac7c3e4ff401 ("compiler: enable
CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline a
function.
It looks like GCC 10 is taking poor decisions on this.
get_order() compiles into the following tiny function, occupying 20
bytes of text.
0000007c <get_order>:
7c: 38 63 ff ff addi r3,r3,-1
80: 54 63 a3 3e rlwinm r3,r3,20,12,31
84: 7c 63 00 34 cntlzw r3,r3
88: 20 63 00 20 subfic r3,r3,32
8c: 4e 80 00 20 blr
By forcing get_order() to be __always_inline, the size of text is
reduced by 1940 bytes, that is almost twice the space occupied by
50 times get_order()
[linux-powerpc]# size vmlinux
text data bss dec hex filename
3840680 675588 135176 4651444 46f9b4 vmlinux
Link: https://lkml.kernel.org/r/96c6172d619c51acc5c1c4884b80785c59af4102.1602949927.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/asm-generic/getorder.h')
| -rw-r--r-- | include/asm-generic/getorder.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h index e9f20b813a69..f2979e3a96b6 100644 --- a/include/asm-generic/getorder.h +++ b/include/asm-generic/getorder.h @@ -26,7 +26,7 @@ * * The result is undefined if the size is 0. */ -static inline __attribute_const__ int get_order(unsigned long size) +static __always_inline __attribute_const__ int get_order(unsigned long size) { if (__builtin_constant_p(size)) { if (!size) |