Messages in this thread | | | Date | Sun, 16 Jun 2013 16:10:41 -0700 | From | Kent Overstreet <> | Subject | Re: [PATCH percpu/for-3.11] percpu-refcount: use RCU-sched insted of normal RCU |
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On Sun, Jun 16, 2013 at 02:55:46PM -0700, Tejun Heo wrote: > 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> > Cc: Kent Overstreet <koverstreet@google.com> > Cc: Michal Hocko <mhocko@suse.cz> > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > Cc: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Kent Overstreet <koverstreet@google.com>
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