Le 19/10/2020 à 06:55, Joel Stanley a écrit :
On Sat, 17 Oct 2020 at 15:55, Christophe Leroy <christophe.le...@csgroup.eu> wrote: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 vmlinuxI see similar results with GCC 10.2 building for arm32. There are 143 instances of get_order with aspeed_g5_defconfig. Before: 9071838 2630138 186468 11888444 b5673c vmlinux After: 9069886 2630126 186468 11886480 b55f90 vmlinux 1952 bytes smaller with your patch applied. Did you raise this with anyone from GCC?
Yes I did, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 For the time being, it's at a standstill. Christophe
Reviewed-by: Joel Stanley <j...@jms.id.au>Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu> --- include/asm-generic/getorder.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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) -- 2.25.0
