b26bf6ab71
The venerable menu governor does some things that are quite questionable in my view. First, it includes timer wakeups in the pattern detection data and mixes them up with wakeups from other sources which in some cases causes it to expect what essentially would be a timer wakeup in a time frame in which no timer wakeups are possible (because it knows the time until the next timer event and that is later than the expected wakeup time). Second, it uses the extra exit latency limit based on the predicted idle duration and depending on the number of tasks waiting on I/O, even though those tasks may run on a different CPU when they are woken up. Moreover, the time ranges used by it for the sleep length correction factors depend on whether or not there are tasks waiting on I/O, which again doesn't imply anything in particular, and they are not correlated to the list of available idle states in any way whatever. Also, the pattern detection code in menu may end up considering values that are too large to matter at all, in which cases running it is a waste of time. A major rework of the menu governor would be required to address these issues and the performance of at least some workloads (tuned specifically to the current behavior of the menu governor) is likely to suffer from that. It is thus better to introduce an entirely new governor without them and let everybody use the governor that works better with their actual workloads. The new governor introduced here, the timer events oriented (TEO) governor, uses the same basic strategy as menu: it always tries to find the deepest idle state that can be used in the given conditions. However, it applies a different approach to that problem. First, it doesn't use "correction factors" for the time till the closest timer, but instead it tries to correlate the measured idle duration values with the available idle states and use that information to pick up the idle state that is most likely to "match" the upcoming CPU idle interval. Second, it doesn't take the number of "I/O waiters" into account at all and the pattern detection code in it avoids taking timer wakeups into account. It also only uses idle duration values less than the current time till the closest timer (with the tick excluded) for that purpose. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
58 lines
1.4 KiB
Plaintext
58 lines
1.4 KiB
Plaintext
menu "CPU Idle"
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config CPU_IDLE
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bool "CPU idle PM support"
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default y if ACPI || PPC_PSERIES
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select CPU_IDLE_GOV_LADDER if (!NO_HZ && !NO_HZ_IDLE)
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select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE) && !CPU_IDLE_GOV_TEO
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help
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CPU idle is a generic framework for supporting software-controlled
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idle processor power management. It includes modular cross-platform
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governors that can be swapped during runtime.
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If you're using an ACPI-enabled platform, you should say Y here.
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if CPU_IDLE
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config CPU_IDLE_MULTIPLE_DRIVERS
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bool
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config CPU_IDLE_GOV_LADDER
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bool "Ladder governor (for periodic timer tick)"
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config CPU_IDLE_GOV_MENU
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bool "Menu governor (for tickless system)"
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config CPU_IDLE_GOV_TEO
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bool "Timer events oriented (TEO) governor (for tickless systems)"
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help
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This governor implements a simplified idle state selection method
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focused on timer events and does not do any interactivity boosting.
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Some workloads benefit from using it and it generally should be safe
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to use. Say Y here if you are not happy with the alternatives.
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config DT_IDLE_STATES
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bool
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menu "ARM CPU Idle Drivers"
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depends on ARM || ARM64
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source "drivers/cpuidle/Kconfig.arm"
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endmenu
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menu "MIPS CPU Idle Drivers"
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depends on MIPS
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source "drivers/cpuidle/Kconfig.mips"
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endmenu
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menu "POWERPC CPU Idle Drivers"
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depends on PPC
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source "drivers/cpuidle/Kconfig.powerpc"
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endmenu
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endif
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config ARCH_NEEDS_CPU_IDLE_COUPLED
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def_bool n
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endmenu
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