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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-06-21 22:08:45 +0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-08-19 05:07:02 +0400
commitb44379af1cf40050794832c38ea6a64e07eb5087 (patch)
tree2f7fb3764976a4a0e2d2cf7a7f814564361203a4 /kernel/time
parent8bdf7a252b6398dbd4beaa7a2ba0904cea0abd04 (diff)
downloadlinux-b44379af1cf40050794832c38ea6a64e07eb5087.tar.xz
nohz_full: Add Kconfig parameter for scalable detection of all-idle state
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 <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> [ paulmck: Update help text per Frederic Weisbecker. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/Kconfig23
1 files changed, 23 insertions, 0 deletions
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 70f27e89012b..c7d2fd67799e 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" 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
bool "Old Idle dynticks config"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS