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authorTejun Heo <tj@kernel.org>2013-06-16 16:12:26 -0700
committerTejun Heo <tj@kernel.org>2013-06-16 16:12:26 -0700
commita4244454df1296e90cc961c1b636b1176ef0d9a0 (patch)
tree9be151f1e7a791dbf2d146fc5283ed246562d7f1 /lib/percpu-refcount.c
parentdbece3a0f1ef0b19aff1cc6ed0942fec9ab98de1 (diff)
downloadlwn-a4244454df1296e90cc961c1b636b1176ef0d9a0.tar.gz
lwn-a4244454df1296e90cc961c1b636b1176ef0d9a0.zip
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>
Diffstat (limited to 'lib/percpu-refcount.c')
-rw-r--r--lib/percpu-refcount.c2
1 files changed, 1 insertions, 1 deletions
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);
}