diff options
author | Tejun Heo <tj@kernel.org> | 2013-06-16 19:12:26 -0400 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2013-06-16 19:12:26 -0400 |
commit | a4244454df1296e90cc961c1b636b1176ef0d9a0 (patch) | |
tree | 9be151f1e7a791dbf2d146fc5283ed246562d7f1 | |
parent | dbece3a0f1ef0b19aff1cc6ed0942fec9ab98de1 (diff) |
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) | |||
105 | { | 105 | { |
106 | unsigned __percpu *pcpu_count; | 106 | unsigned __percpu *pcpu_count; |
107 | 107 | ||
108 | rcu_read_lock(); | 108 | rcu_read_lock_sched(); |
109 | 109 | ||
110 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); | 110 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); |
111 | 111 | ||
@@ -114,7 +114,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref) | |||
114 | else | 114 | else |
115 | atomic_inc(&ref->count); | 115 | atomic_inc(&ref->count); |
116 | 116 | ||
117 | rcu_read_unlock(); | 117 | rcu_read_unlock_sched(); |
118 | } | 118 | } |
119 | 119 | ||
120 | /** | 120 | /** |
@@ -134,7 +134,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) | |||
134 | unsigned __percpu *pcpu_count; | 134 | unsigned __percpu *pcpu_count; |
135 | int ret = false; | 135 | int ret = false; |
136 | 136 | ||
137 | rcu_read_lock(); | 137 | rcu_read_lock_sched(); |
138 | 138 | ||
139 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); | 139 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); |
140 | 140 | ||
@@ -143,7 +143,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) | |||
143 | ret = true; | 143 | ret = true; |
144 | } | 144 | } |
145 | 145 | ||
146 | rcu_read_unlock(); | 146 | rcu_read_unlock_sched(); |
147 | 147 | ||
148 | return ret; | 148 | return ret; |
149 | } | 149 | } |
@@ -159,7 +159,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) | |||
159 | { | 159 | { |
160 | unsigned __percpu *pcpu_count; | 160 | unsigned __percpu *pcpu_count; |
161 | 161 | ||
162 | rcu_read_lock(); | 162 | rcu_read_lock_sched(); |
163 | 163 | ||
164 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); | 164 | pcpu_count = ACCESS_ONCE(ref->pcpu_count); |
165 | 165 | ||
@@ -168,7 +168,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) | |||
168 | else if (unlikely(atomic_dec_and_test(&ref->count))) | 168 | else if (unlikely(atomic_dec_and_test(&ref->count))) |
169 | ref->release(ref); | 169 | ref->release(ref); |
170 | 170 | ||
171 | rcu_read_unlock(); | 171 | rcu_read_unlock_sched(); |
172 | } | 172 | } |
173 | 173 | ||
174 | #endif | 174 | #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, | |||
154 | (((unsigned long) ref->pcpu_count)|PCPU_REF_DEAD); | 154 | (((unsigned long) ref->pcpu_count)|PCPU_REF_DEAD); |
155 | ref->confirm_kill = confirm_kill; | 155 | ref->confirm_kill = confirm_kill; |
156 | 156 | ||
157 | call_rcu(&ref->rcu, percpu_ref_kill_rcu); | 157 | call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu); |
158 | } | 158 | } |