58a6d5f24f
commit 5486f5bf790b5c664913076c3194b8f916a5c7ad upstream.
All functions defined as static inline in net/checksum.h are
meant to be inlined for performance reason.
But since commit ac7c3e4ff401 ("compiler: enable
CONFIG_OPTIMIZE_INLINING forcibly") the compiler is allowed to
uninline functions when it wants.
Fair enough in the general case, but for tiny performance critical
checksum helpers that's counter-productive.
The problem mainly arises when selecting CONFIG_CC_OPTIMISE_FOR_SIZE,
Those helpers being 'static inline' in header files you suddenly find
them duplicated many times in the resulting vmlinux.
Here is a typical exemple when building powerpc pmac32_defconfig
with CONFIG_CC_OPTIMISE_FOR_SIZE. csum_sub() appears 4 times:
c04a23cc <csum_sub>:
c04a23cc: 7c 84 20 f8 not r4,r4
c04a23d0: 7c 63 20 14 addc r3,r3,r4
c04a23d4: 7c 63 01 94 addze r3,r3
c04a23d8: 4e 80 00 20 blr
...
c04a2ce8: 4b ff f6 e5 bl c04a23cc <csum_sub>
...
c04a2d2c: 4b ff f6 a1 bl c04a23cc <csum_sub>
...
c04a2d54: 4b ff f6 79 bl c04a23cc <csum_sub>
...
c04a754c <csum_sub>:
c04a754c: 7c 84 20 f8 not r4,r4
c04a7550: 7c 63 20 14 addc r3,r3,r4
c04a7554: 7c 63 01 94 addze r3,r3
c04a7558: 4e 80 00 20 blr
...
c04ac930: 4b ff ac 1d bl c04a754c <csum_sub>
...
c04ad264: 4b ff a2 e9 bl c04a754c <csum_sub>
...
c04e3b08 <csum_sub>:
c04e3b08: 7c 84 20 f8 not r4,r4
c04e3b0c: 7c 63 20 14 addc r3,r3,r4
c04e3b10: 7c 63 01 94 addze r3,r3
c04e3b14: 4e 80 00 20 blr
...
c04e5788: 4b ff e3 81 bl c04e3b08 <csum_sub>
...
c04e65c8: 4b ff d5 41 bl c04e3b08 <csum_sub>
...
c0512d34 <csum_sub>:
c0512d34: 7c 84 20 f8 not r4,r4
c0512d38: 7c 63 20 14 addc r3,r3,r4
c0512d3c: 7c 63 01 94 addze r3,r3
c0512d40: 4e 80 00 20 blr
...
c0512dfc: 4b ff ff 39 bl c0512d34 <csum_sub>
...
c05138bc: 4b ff f4 79 bl c0512d34 <csum_sub>
...
Restore the expected behaviour by using __always_inline for all
functions defined in net/checksum.h
vmlinux size is even reduced by 256 bytes with this patch:
text data bss dec hex filename
6980022 2515362 194384 9689768 93daa8 vmlinux.before
6979862 2515266 194384 9689512 93d9a8 vmlinux.now
Fixes: ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING forcibly")
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.