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

From: Paul E. McKenney
Date: Fri Jun 08 2012 - 00:27:28 EST


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

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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Tested-by: Pascal Chapperon <pascal.chapperon@xxxxxxxxxx>
---
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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