linux-kernel - [PATCH RFC tip/core/rcu 5/5] rcu: Limit expedited helping to every 10 ms or every 4th GP

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Message-Id: <1435700910-9104-5-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 30 Jun 2015 14:48:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 5/5] rcu: Limit expedited helping to every 10 ms or every 4th GP

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 308b6acb4260..247aa1120c4c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3505,10 +3505,19 @@ void synchronize_sched_expedited(void)
 			   !atomic_read(&rsp->expedited_need_qs));
 
 	rcu_exp_gp_seq_end(rsp);
-	mutex_unlock(&rnp->exp_funnel_mutex);
 	smp_mb(); /* ensure subsequent action seen after grace period. */
-	if (rsp->gp_kthread && rcu_gp_in_progress(rsp))
-		wake_up(&rsp->gp_wq);
+	if (rsp->gp_kthread && rcu_gp_in_progress(rsp)) {
+		static unsigned long nextgp;
+		static unsigned long nextjiffy;
+
+		if (time_after_eq(jiffies, nextgp) ||
+		    ULONG_CMP_GE(rsp->gpnum, nextgp)) {
+			nextgp = rsp->gpnum + 4;
+			nextjiffy = jiffies + 10;
+			wake_up(&rsp->gp_wq);
+		}
+	}
+	mutex_unlock(&rnp->exp_funnel_mutex);
 
 	put_online_cpus();
 }
-- 
1.8.1.5

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