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author | Peter Zijlstra <peterz@infradead.org> | 2013-11-19 16:13:38 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2014-01-13 13:47:36 +0100 |
commit | 9ea4c380066fbe23fe0da7f4abfabc444f2467f4 (patch) | |
tree | a6f3e8def29275f04b33cfb0defcefc9e0adaaf0 /include/linux/rwlock_api_smp.h | |
parent | c726099ec224be8078d91072207053ff9a1ad6fc (diff) | |
download | linux-stable-9ea4c380066fbe23fe0da7f4abfabc444f2467f4.tar.gz linux-stable-9ea4c380066fbe23fe0da7f4abfabc444f2467f4.tar.bz2 linux-stable-9ea4c380066fbe23fe0da7f4abfabc444f2467f4.zip |
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 <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: rui.zhang@intel.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/rwlock_api_smp.h')
-rw-r--r-- | include/linux/rwlock_api_smp.h | 12 |
1 files changed, 4 insertions, 8 deletions
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 */ |