From 9ea4c380066fbe23fe0da7f4abfabc444f2467f4 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 19 Nov 2013 16:13:38 +0100 Subject: locking: Optimize lock_bh functions Currently all _bh_ lock functions do two preempt_count operations: local_bh_disable(); preempt_disable(); and for the unlock: preempt_enable_no_resched(); local_bh_enable(); Since its a waste of perfectly good cycles to modify the same variable twice when you can do it in one go; use the new __local_bh_{dis,en}able_ip() functions that allow us to provide a preempt_count value to add/sub. So define SOFTIRQ_LOCK_OFFSET as the offset a _bh_ lock needs to add/sub to be done in one go. As a bonus it gets rid of the preempt_enable_no_resched() usage. This reduces a 1000 loops of: spin_lock_bh(&bh_lock); spin_unlock_bh(&bh_lock); from 53596 cycles to 51995 cycles. I didn't do enough measurements to say for absolute sure that the result is significant but the the few runs I did for each suggest it is so. Reviewed-by: Thomas Gleixner Signed-off-by: Peter Zijlstra Cc: jacob.jun.pan@linux.intel.com Cc: Mike Galbraith Cc: hpa@zytor.com Cc: Arjan van de Ven Cc: lenb@kernel.org Cc: rjw@rjwysocki.net Cc: rui.zhang@intel.com Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- include/linux/preempt_mask.h | 15 +++++++++++++++ include/linux/rwlock_api_smp.h | 12 ++++-------- include/linux/spinlock_api_smp.h | 12 ++++-------- include/linux/spinlock_api_up.h | 16 +++++++++++----- kernel/softirq.c | 4 ++-- 5 files changed, 36 insertions(+), 23 deletions(-) diff --git a/include/linux/preempt_mask.h b/include/linux/preempt_mask.h index d169820203dd..b8d96bca4357 100644 --- a/include/linux/preempt_mask.h +++ b/include/linux/preempt_mask.h @@ -78,6 +78,21 @@ # define PREEMPT_CHECK_OFFSET 0 #endif +/* + * The preempt_count offset needed for things like: + * + * spin_lock_bh() + * + * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and + * softirqs, such that unlock sequences of: + * + * spin_unlock(); + * local_bh_enable(); + * + * Work as expected. + */ +#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_CHECK_OFFSET) + /* * Are we running in atomic context? WARNING: this macro cannot * always detect atomic context; in particular, it cannot know about diff --git a/include/linux/rwlock_api_smp.h b/include/linux/rwlock_api_smp.h index 9c9f0495d37c..5b9b84b20407 100644 --- a/include/linux/rwlock_api_smp.h +++ b/include/linux/rwlock_api_smp.h @@ -172,8 +172,7 @@ static inline void __raw_read_lock_irq(rwlock_t *lock) static inline void __raw_read_lock_bh(rwlock_t *lock) { - local_bh_disable(); - preempt_disable(); + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_); LOCK_CONTENDED(lock, do_raw_read_trylock, do_raw_read_lock); } @@ -200,8 +199,7 @@ static inline void __raw_write_lock_irq(rwlock_t *lock) static inline void __raw_write_lock_bh(rwlock_t *lock) { - local_bh_disable(); - preempt_disable(); + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_); LOCK_CONTENDED(lock, do_raw_write_trylock, do_raw_write_lock); } @@ -250,8 +248,7 @@ static inline void __raw_read_unlock_bh(rwlock_t *lock) { rwlock_release(&lock->dep_map, 1, _RET_IP_); do_raw_read_unlock(lock); - preempt_enable_no_resched(); - local_bh_enable_ip((unsigned long)__builtin_return_address(0)); + __local_bh_enable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); } static inline void __raw_write_unlock_irqrestore(rwlock_t *lock, @@ -275,8 +272,7 @@ static inline void __raw_write_unlock_bh(rwlock_t *lock) { rwlock_release(&lock->dep_map, 1, _RET_IP_); do_raw_write_unlock(lock); - preempt_enable_no_resched(); - local_bh_enable_ip((unsigned long)__builtin_return_address(0)); + __local_bh_enable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); } #endif /* __LINUX_RWLOCK_API_SMP_H */ diff --git a/include/linux/spinlock_api_smp.h b/include/linux/spinlock_api_smp.h index bdb9993f0fda..42dfab89e740 100644 --- a/include/linux/spinlock_api_smp.h +++ b/include/linux/spinlock_api_smp.h @@ -131,8 +131,7 @@ static inline void __raw_spin_lock_irq(raw_spinlock_t *lock) static inline void __raw_spin_lock_bh(raw_spinlock_t *lock) { - local_bh_disable(); - preempt_disable(); + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); spin_acquire(&lock->dep_map, 0, 0, _RET_IP_); LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock); } @@ -174,20 +173,17 @@ static inline void __raw_spin_unlock_bh(raw_spinlock_t *lock) { spin_release(&lock->dep_map, 1, _RET_IP_); do_raw_spin_unlock(lock); - preempt_enable_no_resched(); - local_bh_enable_ip((unsigned long)__builtin_return_address(0)); + __local_bh_enable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); } static inline int __raw_spin_trylock_bh(raw_spinlock_t *lock) { - local_bh_disable(); - preempt_disable(); + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); if (do_raw_spin_trylock(lock)) { spin_acquire(&lock->dep_map, 0, 1, _RET_IP_); return 1; } - preempt_enable_no_resched(); - local_bh_enable_ip((unsigned long)__builtin_return_address(0)); + __local_bh_enable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET); return 0; } diff --git a/include/linux/spinlock_api_up.h b/include/linux/spinlock_api_up.h index af1f47229e70..d0d188861ad6 100644 --- a/include/linux/spinlock_api_up.h +++ b/include/linux/spinlock_api_up.h @@ -24,11 +24,14 @@ * flags straight, to suppress compiler warnings of unused lock * variables, and to add the proper checker annotations: */ +#define ___LOCK(lock) \ + do { __acquire(lock); (void)(lock); } while (0) + #define __LOCK(lock) \ - do { preempt_disable(); __acquire(lock); (void)(lock); } while (0) + do { preempt_disable(); ___LOCK(lock); } while (0) #define __LOCK_BH(lock) \ - do { local_bh_disable(); __LOCK(lock); } while (0) + do { __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); ___LOCK(lock); } while (0) #define __LOCK_IRQ(lock) \ do { local_irq_disable(); __LOCK(lock); } while (0) @@ -36,12 +39,15 @@ #define __LOCK_IRQSAVE(lock, flags) \ do { local_irq_save(flags); __LOCK(lock); } while (0) +#define ___UNLOCK(lock) \ + do { __release(lock); (void)(lock); } while (0) + #define __UNLOCK(lock) \ - do { preempt_enable(); __release(lock); (void)(lock); } while (0) + do { preempt_enable(); ___UNLOCK(lock); } while (0) #define __UNLOCK_BH(lock) \ - do { preempt_enable_no_resched(); local_bh_enable(); \ - __release(lock); (void)(lock); } while (0) + do { __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); \ + ___UNLOCK(lock); } while (0) #define __UNLOCK_IRQ(lock) \ do { local_irq_enable(); __UNLOCK(lock); } while (0) diff --git a/kernel/softirq.c b/kernel/softirq.c index 11025ccc06dd..7500cce1ebfd 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -107,7 +107,7 @@ static void __local_bh_disable(unsigned long ip, unsigned int cnt) /* * Were softirqs turned off above: */ - if (softirq_count() == cnt) + if (softirq_count() == (cnt & SOFTIRQ_MASK)) trace_softirqs_off(ip); raw_local_irq_restore(flags); @@ -133,7 +133,7 @@ static void __local_bh_enable(unsigned int cnt) { WARN_ON_ONCE(!irqs_disabled()); - if (softirq_count() == cnt) + if (softirq_count() == (cnt & SOFTIRQ_MASK)) trace_softirqs_on(_RET_IP_); preempt_count_sub(cnt); } -- cgit v1.2.3-58-ga151