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author | Tejun Heo <tj@kernel.org> | 2013-06-17 03:12:26 +0400 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2013-06-17 03:12:26 +0400 |
commit | a4244454df1296e90cc961c1b636b1176ef0d9a0 (patch) | |
tree | 9be151f1e7a791dbf2d146fc5283ed246562d7f1 | |
parent | dbece3a0f1ef0b19aff1cc6ed0942fec9ab98de1 (diff) | |
download | linux-a4244454df1296e90cc961c1b636b1176ef0d9a0.tar.xz |
percpu-refcount: use RCU-sched insted of normal RCU
percpu-refcount was incorrectly using preempt_disable/enable() for RCU
critical sections against call_rcu(). 6a24474da8 ("percpu-refcount:
consistently use plain (non-sched) RCU") fixed it by converting the
preepmtion operations with rcu_read_[un]lock() citing that there isn't
any advantage in using sched-RCU over using the usual one; however,
rcu_read_[un]lock() for the preemptible RCU implementation -
CONFIG_TREE_PREEMPT_RCU, chosen when CONFIG_PREEMPT - are slightly
more expensive than preempt_disable/enable().
In a contrived microbench which repeats the followings,
- percpu_ref_get()
- copy 32 bytes of data into percpu buffer
- percpu_put_get()
- copy 32 bytes of data into percpu buffer
rcu_read_[un]lock() used in percpu_ref_get/put() makes it go slower by
about 15% when compared to using sched-RCU.
As the RCU critical sections are extremely short, using sched-RCU
shouldn't have any latency implications. Convert to RCU-sched.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Kent Overstreet <koverstreet@google.com>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r-- | include/linux/percpu-refcount.h | 12 | ||||
-rw-r--r-- | lib/percpu-refcount.c | 2 |
2 files changed, 7 insertions, 7 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index dd2a08600453..95961f0bf62d 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -105,7 +105,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref) { unsigned __percpu *pcpu_count; - rcu_read_lock(); + rcu_read_lock_sched(); pcpu_count = ACCESS_ONCE(ref->pcpu_count); @@ -114,7 +114,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref) else atomic_inc(&ref->count); - rcu_read_unlock(); + rcu_read_unlock_sched(); } /** @@ -134,7 +134,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) unsigned __percpu *pcpu_count; int ret = false; - rcu_read_lock(); + rcu_read_lock_sched(); pcpu_count = ACCESS_ONCE(ref->pcpu_count); @@ -143,7 +143,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) ret = true; } - rcu_read_unlock(); + rcu_read_unlock_sched(); return ret; } @@ -159,7 +159,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) { unsigned __percpu *pcpu_count; - rcu_read_lock(); + rcu_read_lock_sched(); pcpu_count = ACCESS_ONCE(ref->pcpu_count); @@ -168,7 +168,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) else if (unlikely(atomic_dec_and_test(&ref->count))) ref->release(ref); - rcu_read_unlock(); + rcu_read_unlock_sched(); } #endif diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 8bf9e719cca0..7deeb6297a48 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -154,5 +154,5 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref, (((unsigned long) ref->pcpu_count)|PCPU_REF_DEAD); ref->confirm_kill = confirm_kill; - call_rcu(&ref->rcu, percpu_ref_kill_rcu); + call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu); } |