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authorPeter Zijlstra <peterz@infradead.org>2013-11-19 16:13:38 +0100
committerIngo Molnar <mingo@kernel.org>2014-01-13 13:47:36 +0100
commit9ea4c380066fbe23fe0da7f4abfabc444f2467f4 (patch)
treea6f3e8def29275f04b33cfb0defcefc9e0adaaf0 /include/linux/spinlock_api_smp.h
parentc726099ec224be8078d91072207053ff9a1ad6fc (diff)
downloadlwn-9ea4c380066fbe23fe0da7f4abfabc444f2467f4.tar.gz
lwn-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/spinlock_api_smp.h')
-rw-r--r--include/linux/spinlock_api_smp.h12
1 files changed, 4 insertions, 8 deletions
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;
}