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* [PATCH] force inlining of spinlock ops
@ 2015-07-13 18:31 Denys Vlasenko
  2015-07-21  9:41 ` [tip:x86/asm] locking/spinlocks: Force " tip-bot for Denys Vlasenko
  0 siblings, 1 reply; 2+ messages in thread
From: Denys Vlasenko @ 2015-07-13 18:31 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: Denys Vlasenko, Thomas Graf, Bart Van Assche, Peter Zijlstra,
	David Rientjes, Andrew Morton, Paul E. McKenney, linux-kernel

With both gcc 4.7.2 and 4.9.2, 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

In particular,
with this config: http://busybox.net/~vda/kernel_config
there are more than a thousand copies of tiny spinlock-related functions:

$ nm --size-sort vmlinux | grep -iF ' t ' | uniq -c | grep -v '^ *1 ' | sort -rn | grep ' spin'
    473 000000000000000b t spin_unlock_irqrestore
    292 000000000000000b t spin_unlock
    215 000000000000000b t spin_lock
    134 000000000000000b t spin_unlock_irq
    130 000000000000000b t spin_unlock_bh
    120 000000000000000b t spin_lock_irq
    106 000000000000000b t spin_lock_bh

Disassembly:

ffffffff81004720 <spin_lock>:
ffffffff81004720:       55                      push   %rbp
ffffffff81004721:       48 89 e5                mov    %rsp,%rbp
ffffffff81004724:       e8 f8 4e e2 02          callq  <_raw_spin_lock>
ffffffff81004729:       5d                      pop    %rbp
ffffffff8100472a:       c3                      retq

This patch fixes this via s/inline/__always_inline/ in spinlock.h.
This decreases vmlinux by about 40k:

    text     data      bss       dec     hex filename
82375570 22255544 20627456 125258570 7774b4a vmlinux.before
82335059 22255416 20627456 125217931 776ac8b vmlinux

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org
---
 include/linux/spinlock.h | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 3e18379..073925d 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -296,7 +296,7 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
  * Map the spin_lock functions to the raw variants for PREEMPT_RT=n
  */
 
-static inline raw_spinlock_t *spinlock_check(spinlock_t *lock)
+static __always_inline raw_spinlock_t *spinlock_check(spinlock_t *lock)
 {
 	return &lock->rlock;
 }
@@ -307,17 +307,17 @@ do {							\
 	raw_spin_lock_init(&(_lock)->rlock);		\
 } while (0)
 
-static inline void spin_lock(spinlock_t *lock)
+static __always_inline void spin_lock(spinlock_t *lock)
 {
 	raw_spin_lock(&lock->rlock);
 }
 
-static inline void spin_lock_bh(spinlock_t *lock)
+static __always_inline void spin_lock_bh(spinlock_t *lock)
 {
 	raw_spin_lock_bh(&lock->rlock);
 }
 
-static inline int spin_trylock(spinlock_t *lock)
+static __always_inline int spin_trylock(spinlock_t *lock)
 {
 	return raw_spin_trylock(&lock->rlock);
 }
@@ -337,7 +337,7 @@ do {									\
 	raw_spin_lock_nest_lock(spinlock_check(lock), nest_lock);	\
 } while (0)
 
-static inline void spin_lock_irq(spinlock_t *lock)
+static __always_inline void spin_lock_irq(spinlock_t *lock)
 {
 	raw_spin_lock_irq(&lock->rlock);
 }
@@ -352,32 +352,32 @@ do {									\
 	raw_spin_lock_irqsave_nested(spinlock_check(lock), flags, subclass); \
 } while (0)
 
-static inline void spin_unlock(spinlock_t *lock)
+static __always_inline void spin_unlock(spinlock_t *lock)
 {
 	raw_spin_unlock(&lock->rlock);
 }
 
-static inline void spin_unlock_bh(spinlock_t *lock)
+static __always_inline void spin_unlock_bh(spinlock_t *lock)
 {
 	raw_spin_unlock_bh(&lock->rlock);
 }
 
-static inline void spin_unlock_irq(spinlock_t *lock)
+static __always_inline void spin_unlock_irq(spinlock_t *lock)
 {
 	raw_spin_unlock_irq(&lock->rlock);
 }
 
-static inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
+static __always_inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
 {
 	raw_spin_unlock_irqrestore(&lock->rlock, flags);
 }
 
-static inline int spin_trylock_bh(spinlock_t *lock)
+static __always_inline int spin_trylock_bh(spinlock_t *lock)
 {
 	return raw_spin_trylock_bh(&lock->rlock);
 }
 
-static inline int spin_trylock_irq(spinlock_t *lock)
+static __always_inline int spin_trylock_irq(spinlock_t *lock)
 {
 	return raw_spin_trylock_irq(&lock->rlock);
 }
@@ -387,22 +387,22 @@ static inline int spin_trylock_irq(spinlock_t *lock)
 	raw_spin_trylock_irqsave(spinlock_check(lock), flags); \
 })
 
-static inline void spin_unlock_wait(spinlock_t *lock)
+static __always_inline void spin_unlock_wait(spinlock_t *lock)
 {
 	raw_spin_unlock_wait(&lock->rlock);
 }
 
-static inline int spin_is_locked(spinlock_t *lock)
+static __always_inline int spin_is_locked(spinlock_t *lock)
 {
 	return raw_spin_is_locked(&lock->rlock);
 }
 
-static inline int spin_is_contended(spinlock_t *lock)
+static __always_inline int spin_is_contended(spinlock_t *lock)
 {
 	return raw_spin_is_contended(&lock->rlock);
 }
 
-static inline int spin_can_lock(spinlock_t *lock)
+static __always_inline int spin_can_lock(spinlock_t *lock)
 {
 	return raw_spin_can_lock(&lock->rlock);
 }
-- 
1.8.1.4


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2015-07-13 18:31 [PATCH] force inlining of spinlock ops Denys Vlasenko
2015-07-21  9:41 ` [tip:x86/asm] locking/spinlocks: Force " tip-bot for Denys Vlasenko

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