linux-kernel - [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

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Message-Id: <1484708037-2523-7-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Tue, 17 Jan 2017 18:53:46 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.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 v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
frequent calls to resched_cpu(), which means that the only time
resched_cpu() is invoked is after an RCU CPU stall warning.  Although
this is good from an avoid-IPIs perspective, we should try to break
things loose -before- splatting.  This commit therefore starts invoking
resched_cpu() for each holdout at each force-quiescent-state interval
that is more than halfway through the stall-warning interval.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 83bf054e194e..0e61b62e3f4a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
 	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
 		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
+	/*
+	 * If more than halfway to RCU CPU stall-warning time, do
+	 * a resched_cpu() to try to loosen things up a bit.
+	 */
+	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
+		resched_cpu(rdp->cpu);
 
 	return 0;
 }
-- 
2.5.2