Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

"
 * Update RCU documentation.  These were posted to LKML at
   https://lkml.org/lkml/2013/8/19/611.

 * Miscellaneous fixes.  These were posted to LKML at
   https://lkml.org/lkml/2013/8/19/619.

 * Full-system idle detection.  This is for use by Frederic
   Weisbecker's adaptive-ticks mechanism.  Its purpose is
   to allow the timekeeping CPU to shut off its tick when
   all other CPUs are idle.  These were posted to LKML at
   https://lkml.org/lkml/2013/8/19/648.

 * Improve rcutorture test coverage.  These were posted to LKML at
   https://lkml.org/lkml/2013/8/19/675.
"

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 50 insertions, 0 deletions

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 70f27e89012b..3381f098070f 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -134,6 +134,56 @@ config NO_HZ_FULL_ALL
          Note the boot CPU will still be kept outside the range to
          handle the timekeeping duty.
 
+config NO_HZ_FULL_SYSIDLE
+        bool "Detect full-system idle state for full dynticks system"
+        depends on NO_HZ_FULL
+        default n
+        help
+         At least one CPU must keep the scheduling-clock tick running for
+         timekeeping purposes whenever there is a non-idle CPU, where
+         "non-idle" also includes dynticks CPUs as long as they are
+         running non-idle tasks.  Because the underlying adaptive-tick
+         support cannot distinguish between all CPUs being idle and
+         all CPUs each running a single task in dynticks mode, the
+         underlying support simply ensures that there is always a CPU
+         handling the scheduling-clock tick, whether or not all CPUs
+         are idle.  This Kconfig option enables scalable detection of
+         the all-CPUs-idle state, thus allowing the scheduling-clock
+         tick to be disabled when all CPUs are idle.  Note that scalable
+         detection of the all-CPUs-idle state means that larger systems
+         will be slower to declare the all-CPUs-idle state.
+
+         Say Y if you would like to help debug all-CPUs-idle detection.
+
+         Say N if you are unsure.
+
+config NO_HZ_FULL_SYSIDLE_SMALL
+        int "Number of CPUs above which large-system approach is used"
+        depends on NO_HZ_FULL_SYSIDLE
+        range 1 NR_CPUS
+        default 8
+        help
+         The full-system idle detection mechanism takes a lazy approach
+         on large systems, as is required to attain decent scalability.
+         However, on smaller systems, scalability is not anywhere near as
+         large a concern as is energy efficiency.  The sysidle subsystem
+         therefore uses a fast but non-scalable algorithm for small
+         systems and a lazier but scalable algorithm for large systems.
+         This Kconfig parameter defines the number of CPUs in the largest
+         system that will be considered to be "small".
+
+         The default value will be fine in most cases.  Battery-powered
+         systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
+         numbers of CPUs, and (3) are suffering from battery-lifetime
+         problems due to long sysidle latencies might wish to experiment
+         with larger values for this Kconfig parameter.  On the other
+         hand, they might be even better served by disabling NO_HZ_FULL
+         entirely, given that NO_HZ_FULL is intended for HPC and
+         real-time workloads that at present do not tend to be run on
+         battery-powered systems.
+
+         Take the default if you are unsure.
+
 config NO_HZ
         bool "Old Idle dynticks config"
         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS