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rcu: substitute set_need_resched for sending resched IPIs 

This patch adds a check to __rcu_pending() that does a local
set_need_resched() if the current CPU is holding up the current grace
period and if force_quiescent_state() will be called soon.  The goal is
to reduce the probability that force_quiescent_state() will need to do
smp_send_reschedule(), which sends an IPI and is therefore more expensive
on most architectures.

Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2010-03-18 21:36:51 -07:00
parent 2b3fc35f69
commit d25eb9442b
1 changed files with 10 additions and 0 deletions
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10
kernel/rcutree.c
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@ -1499,6 +1499,16 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rdp->qs_pending) {
/*
* If force_quiescent_state() coming soon and this CPU
* needs a quiescent state, and this is either RCU-sched
* or RCU-bh, force a local reschedule.
*/
if (!rdp->preemptable &&
ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
jiffies))
set_need_resched();
rdp->n_rp_qs_pending++;
return 1;
}