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[PATCH v2 tip/core/rcu 0/11] Expedited-grace-period changes for 4.5

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  [PATCH v2 tip/core/rcu 0/11] Expedited-grace-period changes for 4.5 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-10 00:10 +0100
    [PATCH v2 tip/core/rcu 06/11] rcu: Make expedited grace periods resolve stall-warning ties "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-10 00:10 +0100

#1287997 — [PATCH v2 tip/core/rcu 0/11] Expedited-grace-period changes for 4.5

Hello!

This series contains follow-on cleanup changes to RCU's expedited
grace-period functionality.  The patches in this series are as follows:

1.	Short-circuit synchronize_sched_expedited() if there is only one CPU.

2.	Update comment to clarify the role of ->expmaskinitnext.

3.	Separate concerns by moving smp_mb() from rcu_seq_snap() to
	rcu_exp_gp_seq_snap().

4.	Safe a few lines of code by inverting the sense of
	sync_rcu_exp_select_cpus() "if" statement.

5.	Reduce expedited GP memory contention via per-CPU variables.

6.	Get rid of (some) empty stall-warning messages by resolving
	stall-warning ties.

7.	Add more diagnostics to expedited stall warning messages.

8.	Add rcu_normal kernel parameter to suppress expediting for
	the benefit of aggressive real-time systems.

9-10.	Allow expedited grace periods to be disabled just before init
	is spawned, allowing them to speed up boot without interfering
	with run-time real-time workloads.

11.	Remove TINY_RCU bloat from pointless (to TINY_RCU) boot parameters.

Changes since v1:

o	Add patch 11 removing TINY_RCU bloat.

o	Get cover letter and patches correctly associated.  :-/

							Thanx, Paul

------------------------------------------------------------------------

 Documentation/kernel-parameters.txt |   37 ++++++++++++----
 include/linux/rcupdate.h            |   15 ++++++
 init/main.c                         |    2 
 kernel/ksysfs.c                     |   26 ++++++++++-
 kernel/rcu/srcu.c                   |    2 
 kernel/rcu/tree.c                   |   79 +++++++++++++++++++++++-------------
 kernel/rcu/tree.h                   |   10 ++--
 kernel/rcu/tree_plugin.h            |    6 ++
 kernel/rcu/tree_trace.c             |   18 +++++---
 kernel/rcu/update.c                 |   24 +++++++++-
 10 files changed, 165 insertions(+), 54 deletions(-)

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#1287998 — [PATCH v2 tip/core/rcu 06/11] rcu: Make expedited grace periods resolve stall-warning ties

Currently, if a grace period ends just as the stall-warning timeout
fires, an empty stall warning will be printed.  This is not helpful,
so this commit avoids these useless warnings by rechecking completion
after awakening in synchronize_sched_expedited_wait().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 33d7e2551165..bc6b79716a86 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3757,7 +3757,7 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
 				rsp->expedited_wq,
 				sync_rcu_preempt_exp_done(rnp_root),
 				jiffies_stall);
-		if (ret > 0)
+		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
 			return;
 		if (ret < 0) {
 			/* Hit a signal, disable CPU stall warnings. */
-- 
2.5.2

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