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rcu: Prevent early boot set_need_resched() from __rcu_pending() 

There isn't a whole lot of point in poking the scheduler before there
are other tasks to switch to.  This commit therefore adds a check
for rcu_scheduler_fully_active in __rcu_pending() to suppress any
pre-scheduler calls to set_need_resched().  The downside of this approach
is additional runtime overhead in a reasonably hot code path.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-08-04 06:59:03 -07:00 committed by Paul E. McKenney
parent 4627e240df
commit 5c51dd7349
1 changed files with 2 additions and 1 deletions
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3
kernel/rcutree.c
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@ -1707,7 +1707,8 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
check_cpu_stall(rsp, rdp);
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rdp->qs_pending && !rdp->passed_quiesce) {
if (rcu_scheduler_fully_active &&
rdp->qs_pending && !rdp->passed_quiesce) {
/*
* If force_quiescent_state() coming soon and this CPU