linux-kernel - [PATCH] asm-generic: force inlining of some atomic

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Message-Id: <1454615136-32308-1-git-send-email-dvlasenk@redhat.com>
Date:	Thu,  4 Feb 2016 20:45:34 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>, Thomas Graf <tgraf@...g.ch>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] asm-generic: force inlining of some atomic_long operations

Sometimes gcc mysteriously doesn't inline
very small functions we expect to be inlined. See
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122

With this .config:
http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os,
atomic_long_inc(), atomic_long_dec() and atomic_long_add()
functions get deinlined about 40 times. Examples of disassembly:

<atomic_long_inc> (21 copies, 147 calls):
       55                      push   %rbp
       48 89 e5                mov    %rsp,%rbp
       f0 48 ff 07             lock incq (%rdi)
       5d                      pop    %rbp
       c3                      retq

<atomic_long_dec> (4 copies, 14 calls) is similar to inc.

<atomic_long_add> (11 copies, 41 calls):
       55                      push   %rbp
       48 89 e5                mov    %rsp,%rbp
       f0 48 01 3e             lock add %rdi,(%rsi)
       5d                      pop    %rbp
       c3                      retq

This patch fixes this via s/inline/__always_inline/.
Code size decrease after the patch is ~1.3k:

    text     data      bss       dec     hex filename
92203657 20826112 36417536 149447305 8e86289 vmlinux
92202377 20826112 36417536 149446025 8e85d89 vmlinux4_atomiclong_after

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Graf <tgraf@...g.ch>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
---
 include/asm-generic/atomic-long.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/atomic-long.h b/include/asm-generic/atomic-long.h
index eb1973b..5e1f345 100644
--- a/include/asm-generic/atomic-long.h
+++ b/include/asm-generic/atomic-long.h
@@ -98,14 +98,14 @@ ATOMIC_LONG_ADD_SUB_OP(sub, _release)
 #define atomic_long_xchg(v, new) \
 	(ATOMIC_LONG_PFX(_xchg)((ATOMIC_LONG_PFX(_t) *)(v), (new)))
 
-static inline void atomic_long_inc(atomic_long_t *l)
+static __always_inline void atomic_long_inc(atomic_long_t *l)
 {
 	ATOMIC_LONG_PFX(_t) *v = (ATOMIC_LONG_PFX(_t) *)l;
 
 	ATOMIC_LONG_PFX(_inc)(v);
 }
 
-static inline void atomic_long_dec(atomic_long_t *l)
+static __always_inline void atomic_long_dec(atomic_long_t *l)
 {
 	ATOMIC_LONG_PFX(_t) *v = (ATOMIC_LONG_PFX(_t) *)l;
 
@@ -113,7 +113,7 @@ static inline void atomic_long_dec(atomic_long_t *l)
 }
 
 #define ATOMIC_LONG_OP(op)						\
-static inline void							\
+static __always_inline void						\
 atomic_long_##op(long i, atomic_long_t *l)				\
 {									\
 	ATOMIC_LONG_PFX(_t) *v = (ATOMIC_LONG_PFX(_t) *)l;		\
-- 
1.8.1.4