rcu: Simplify rcu_read_unlock_special() quiescent-state accounting
commitc3422bea5f09b0e85704f51f2b01271630b8940b
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Sun, 13 Sep 2009 16:15:10 +0000 (13 09:15 -0700)
committerIngo Molnar <mingo@elte.hu>
Thu, 17 Sep 2009 22:06:33 +0000 (18 00:06 +0200)
treefc4a18241b0f7f5d71211f6787428197769cb9f5
parentb0e165c035b13e1074fa0b555318bd9cb7102558
rcu: Simplify rcu_read_unlock_special() quiescent-state accounting

The earlier approach required two scheduling-clock ticks to note an
preemptable-RCU quiescent state in the situation in which the
scheduling-clock interrupt is unlucky enough to always interrupt an
RCU read-side critical section.

With this change, the quiescent state is instead noted by the
outermost rcu_read_unlock() immediately following the first
scheduling-clock tick, or, alternatively, by the first subsequent
context switch.  Therefore, this change also speeds up grace
periods.

Suggested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference: <12528585111945-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
include/linux/sched.h
kernel/rcutree.c
kernel/rcutree_plugin.h