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Subject[tip:x86/asm] x86/asm/bitops: Force inlining of test_and_set_bit and friends
Commit-ID:  8dd5032d9c540111dd673078738d137a998d6c3f
Gitweb: http://git.kernel.org/tip/8dd5032d9c540111dd673078738d137a998d6c3f
Author: Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Sun, 7 Feb 2016 22:51:27 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 9 Feb 2016 10:31:54 +0100

x86/asm/bitops: Force inlining of test_and_set_bit and friends

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

Arguably, GCC should do better, but GCC people aren't willing
to invest time into it and are asking to use __always_inline
instead.

With this .config:

http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os

here's an example of functions getting deinlined many times:

test_and_set_bit (166 copies, ~1260 calls)
55 push %rbp
48 89 e5 mov %rsp,%rbp
f0 48 0f ab 3e lock bts %rdi,(%rsi)
72 04 jb <test_and_set_bit+0xf>
31 c0 xor %eax,%eax
eb 05 jmp <test_and_set_bit+0x14>
b8 01 00 00 00 mov $0x1,%eax
5d pop %rbp
c3 retq

test_and_clear_bit (124 copies, ~1000 calls)
55 push %rbp
48 89 e5 mov %rsp,%rbp
f0 48 0f b3 3e lock btr %rdi,(%rsi)
72 04 jb <test_and_clear_bit+0xf>
31 c0 xor %eax,%eax
eb 05 jmp <test_and_clear_bit+0x14>
b8 01 00 00 00 mov $0x1,%eax
5d pop %rbp
c3 retq

change_bit (3 copies, 8 calls)
55 push %rbp
48 89 e5 mov %rsp,%rbp
f0 48 0f bb 3e lock btc %rdi,(%rsi)
5d pop %rbp
c3 retq

clear_bit_unlock (2 copies, 11 calls)
55 push %rbp
48 89 e5 mov %rsp,%rbp
f0 48 0f b3 3e lock btr %rdi,(%rsi)
5d pop %rbp
c3 retq

This patch works it around via s/inline/__always_inline/.

Code size decrease by ~13.5k after the patch:

text data bss dec filename
92110727 20826144 36417536 149354407 vmlinux.before
92097234 20826176 36417536 149340946 vmlinux.after

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Graf <tgraf@suug.ch>
Link: http://lkml.kernel.org/r/1454881887-1367-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/bitops.h | 36 ++++++++++++++++++------------------
1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index cfe3b95..7766d1c 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -91,7 +91,7 @@ set_bit(long nr, volatile unsigned long *addr)
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
-static inline void __set_bit(long nr, volatile unsigned long *addr)
+static __always_inline void __set_bit(long nr, volatile unsigned long *addr)
{
asm volatile("bts %1,%0" : ADDR : "Ir" (nr) : "memory");
}
@@ -128,13 +128,13 @@ clear_bit(long nr, volatile unsigned long *addr)
* clear_bit() is atomic and implies release semantics before the memory
* operation. It can be used for an unlock.
*/
-static inline void clear_bit_unlock(long nr, volatile unsigned long *addr)
+static __always_inline void clear_bit_unlock(long nr, volatile unsigned long *addr)
{
barrier();
clear_bit(nr, addr);
}

-static inline void __clear_bit(long nr, volatile unsigned long *addr)
+static __always_inline void __clear_bit(long nr, volatile unsigned long *addr)
{
asm volatile("btr %1,%0" : ADDR : "Ir" (nr));
}
@@ -151,7 +151,7 @@ static inline void __clear_bit(long nr, volatile unsigned long *addr)
* No memory barrier is required here, because x86 cannot reorder stores past
* older loads. Same principle as spin_unlock.
*/
-static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
+static __always_inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
{
barrier();
__clear_bit(nr, addr);
@@ -166,7 +166,7 @@ static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
-static inline void __change_bit(long nr, volatile unsigned long *addr)
+static __always_inline void __change_bit(long nr, volatile unsigned long *addr)
{
asm volatile("btc %1,%0" : ADDR : "Ir" (nr));
}
@@ -180,7 +180,7 @@ static inline void __change_bit(long nr, volatile unsigned long *addr)
* Note that @nr may be almost arbitrarily large; this function is not
* restricted to acting on a single-word quantity.
*/
-static inline void change_bit(long nr, volatile unsigned long *addr)
+static __always_inline void change_bit(long nr, volatile unsigned long *addr)
{
if (IS_IMMEDIATE(nr)) {
asm volatile(LOCK_PREFIX "xorb %1,%0"
@@ -201,7 +201,7 @@ static inline void change_bit(long nr, volatile unsigned long *addr)
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_set_bit(long nr, volatile unsigned long *addr)
+static __always_inline int test_and_set_bit(long nr, volatile unsigned long *addr)
{
GEN_BINARY_RMWcc(LOCK_PREFIX "bts", *addr, "Ir", nr, "%0", "c");
}
@@ -228,7 +228,7 @@ test_and_set_bit_lock(long nr, volatile unsigned long *addr)
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
*/
-static inline int __test_and_set_bit(long nr, volatile unsigned long *addr)
+static __always_inline int __test_and_set_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

@@ -247,7 +247,7 @@ static inline int __test_and_set_bit(long nr, volatile unsigned long *addr)
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_clear_bit(long nr, volatile unsigned long *addr)
+static __always_inline int test_and_clear_bit(long nr, volatile unsigned long *addr)
{
GEN_BINARY_RMWcc(LOCK_PREFIX "btr", *addr, "Ir", nr, "%0", "c");
}
@@ -268,7 +268,7 @@ static inline int test_and_clear_bit(long nr, volatile unsigned long *addr)
* accessed from a hypervisor on the same CPU if running in a VM: don't change
* this without also updating arch/x86/kernel/kvm.c
*/
-static inline int __test_and_clear_bit(long nr, volatile unsigned long *addr)
+static __always_inline int __test_and_clear_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

@@ -280,7 +280,7 @@ static inline int __test_and_clear_bit(long nr, volatile unsigned long *addr)
}

/* WARNING: non atomic and it can be reordered! */
-static inline int __test_and_change_bit(long nr, volatile unsigned long *addr)
+static __always_inline int __test_and_change_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

@@ -300,7 +300,7 @@ static inline int __test_and_change_bit(long nr, volatile unsigned long *addr)
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_change_bit(long nr, volatile unsigned long *addr)
+static __always_inline int test_and_change_bit(long nr, volatile unsigned long *addr)
{
GEN_BINARY_RMWcc(LOCK_PREFIX "btc", *addr, "Ir", nr, "%0", "c");
}
@@ -311,7 +311,7 @@ static __always_inline int constant_test_bit(long nr, const volatile unsigned lo
(addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
}

-static inline int variable_test_bit(long nr, volatile const unsigned long *addr)
+static __always_inline int variable_test_bit(long nr, volatile const unsigned long *addr)
{
int oldbit;

@@ -343,7 +343,7 @@ static int test_bit(int nr, const volatile unsigned long *addr);
*
* Undefined if no bit exists, so code should check against 0 first.
*/
-static inline unsigned long __ffs(unsigned long word)
+static __always_inline unsigned long __ffs(unsigned long word)
{
asm("rep; bsf %1,%0"
: "=r" (word)
@@ -357,7 +357,7 @@ static inline unsigned long __ffs(unsigned long word)
*
* Undefined if no zero exists, so code should check against ~0UL first.
*/
-static inline unsigned long ffz(unsigned long word)
+static __always_inline unsigned long ffz(unsigned long word)
{
asm("rep; bsf %1,%0"
: "=r" (word)
@@ -371,7 +371,7 @@ static inline unsigned long ffz(unsigned long word)
*
* Undefined if no set bit exists, so code should check against 0 first.
*/
-static inline unsigned long __fls(unsigned long word)
+static __always_inline unsigned long __fls(unsigned long word)
{
asm("bsr %1,%0"
: "=r" (word)
@@ -393,7 +393,7 @@ static inline unsigned long __fls(unsigned long word)
* set bit if value is nonzero. The first (least significant) bit
* is at position 1.
*/
-static inline int ffs(int x)
+static __always_inline int ffs(int x)
{
int r;

@@ -434,7 +434,7 @@ static inline int ffs(int x)
* set bit if value is nonzero. The last (most significant) bit is
* at position 32.
*/
-static inline int fls(int x)
+static __always_inline int fls(int x)
{
int r;

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