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>
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@ -134,6 +134,29 @@ config NO_HZ_FULL_ALL
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Note the boot CPU will still be kept outside the range to
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handle the timekeeping duty.
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config NO_HZ_FULL_SYSIDLE
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bool "Detect full-system idle state for full dynticks system"
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depends on NO_HZ_FULL
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default n
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help
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At least one CPU must keep the scheduling-clock tick running for
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timekeeping purposes whenever there is a non-idle CPU, where
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"non-idle" also includes dynticks CPUs as long as they are
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running non-idle tasks. Because the underlying adaptive-tick
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support cannot distinguish between all CPUs being idle and
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all CPUs each running a single task in dynticks mode, the
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underlying support simply ensures that there is always a CPU
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handling the scheduling-clock tick, whether or not all CPUs
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are idle. This Kconfig option enables scalable detection of
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the all-CPUs-idle state, thus allowing the scheduling-clock
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tick to be disabled when all CPUs are idle. Note that scalable
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detection of the all-CPUs-idle state means that larger systems
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will be slower to declare the all-CPUs-idle state.
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Say Y if you would like to help debug all-CPUs-idle detection.
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Say N if you are unsure.
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config NO_HZ
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bool "Old Idle dynticks config"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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