From: Tejun Heo Date: Sun, 16 Jun 2013 23:12:26 +0000 (-0700) Subject: percpu-refcount: use RCU-sched insted of normal RCU X-Git-Tag: omap-for-v3.11/fixes-for-merge-window~46^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a4244454df1296e90cc961c1b636b1176ef0d9a0;p=pandora-kernel.git 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 Acked-by: Kent Overstreet Acked-by: "Paul E. McKenney" Cc: Michal Hocko Cc: Rusty Russell --- Reading git-diff-tree failed