[PATCH] Reduce grace-period-encouragement impact on rcutree __call_rcu()

[Paul E . McKenney]

Remove only the emergency force_quiescent_state() from __call_rcu(),
which should get most of the reduction in overhead while still
allowing the tick to be turned off when non-idle, as proposed in
http://lkml.org/lkml/2009/9/1/229, and which reduced interrupts to
one per ten seconds in a CPU-bound computational workload according to
http://lkml.org/lkml/2009/9/3/7.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcutree.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d2a372f..4c8e0d2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1220,7 +1220,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
 	/* Force the grace period if too many callbacks or too long waiting. */
 	if (unlikely(++rdp->qlen > qhimark)) {
 		rdp->blimit = LONG_MAX;
-		force_quiescent_state(rsp, 0);
 	} else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
 		force_quiescent_state(rsp, 1);
 	local_irq_restore(flags);
-- 
1.5.2.5

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