From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
At least one CPU must keep the scheduling-clock tick running for
timekeeping purposes whenever there is a non-idle CPU. However, with
the new nohz_full adaptive-idle machinery, it is difficult to distinguish
between all CPUs really being idle as opposed to all non-idle CPUs being
in adaptive-ticks mode. This commit therefore adds a Kconfig parameter
as a first step towards enabling a scalable detection of full-system
idle state.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Steven Rostedt <rost...@goodmis.org>
---
kernel/time/Kconfig | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 70f27e8..a613c2a 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -134,6 +134,29 @@ 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" includes CPUs with a single runnable task
+ in adaptive-idle mode. Because the underlying adaptive-tick
+ support cannot distinguish between all CPUs being idle and
+ all CPUs each running a single task in adaptive-idle 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
bool "Old Idle dynticks config"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
--
1.8.1.5
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