linux-kernel - [PATCH rcu 1/8] rcu: RCU_FAST_NO_HZ detection of callback adoption

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Message-Id: <1339129615-1795-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Thu,  7 Jun 2012 21:26:48 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH rcu 1/8] rcu: RCU_FAST_NO_HZ detection of callback adoption

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

In the present implementations of CPU hotplug, the outgoing CPU is
guaranteed to run its stop-machine process on the way out, which
will guarantee that RCU_FAST_NO_HZ forces the CPU out of dyntick-idle
mode.

However, new versions of CPU hotplug might not work this way.  This
commit therefore removes this design constraint by explicitly notifying
CPUs when they adopt non-lazy RCU callbacks.

Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Tested-by: Heiko Carstens <heiko.carstens@...ibm.com>
Tested-by: Pascal Chapperon <pascal.chapperon@...adoo.fr>
---
 kernel/rcutree.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0da7b88..3b0f133 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1397,6 +1397,8 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
 	rdp->qlen_lazy += rsp->qlen_lazy;
 	rdp->qlen += rsp->qlen;
 	rdp->n_cbs_adopted += rsp->qlen;
+	if (rsp->qlen_lazy != rsp->qlen)
+		rcu_idle_count_callbacks_posted();
 	rsp->qlen_lazy = 0;
 	rsp->qlen = 0;
 
-- 
1.7.8

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