89ffd44dfb
Adds event based scheduling logic to the kernel. Updates management of timeouts, timers, idling etc. based on time tracked at events rather than periodic ticks. Provides interfaces for timers to announce and get next timer expiry based on kernel scheduling decisions involving time slicing of threads, timeouts and idling. Uses wall time units instead of ticks in all scheduling activities. The implementation involves changes in the following areas 1. Management of time in wall units like ms/us instead of ticks The existing implementation already had an option to configure number of ticks in a second. The new implementation builds on top of that feature and provides option to set the size of the scheduling granurality to mili seconds or micro seconds. This allows most of the current implementation to be reused. Due to this re-use and co-existence with tick based kernel, the names of variables may contain the word "tick". However, in the tickless kernel implementation, it represents the currently configured time unit, which would be be mili seconds or micro seconds. The APIs that take time as a parameter are not impacted and they continue to pass time in mili seconds. 2. Timers would not be programmed in periodic mode generating ticks. Instead they would be programmed in one shot mode to generate events at the time the kernel scheduler needs to gain control for its scheduling activities like timers, timeouts, time slicing, idling etc. 3. The scheduler provides interfaces that the timer drivers use to announce elapsed time and get the next time the scheduler needs a timer event. It is possible that the scheduler may not need another timer event, in which case the system would wait for a non-timer event to wake it up if it is idling. 4. New APIs are defined to be implemented by timer drivers. Also they need to handler timer events differently. These changes have been done in the HPET timer driver. In future other timers that support tickles kernel should implement these APIs as well. These APIs are to re-program the timer, update and announce elapsed time. 5. Philosopher and timer_api applications have been enabled to test tickless kernel. Separate configuration files are created which define the necessary CONFIG flags. Run these apps using following command make pristine && make BOARD=qemu_x86 CONF_FILE=prj_tickless.conf qemu Jira: ZEP-339 ZEP-1946 ZEP-948 Change-Id: I7d950c31bf1ff929a9066fad42c2f0559a2e5983 Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>
115 lines
4 KiB
Text
115 lines
4 KiB
Text
#
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# Copyright (c) 2014-2015 Wind River Systems, Inc.
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# Copyright (c) 2016 Intel Corporation
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#
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# SPDX-License-Identifier: Apache-2.0
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#
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menuconfig SYS_POWER_MANAGEMENT
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bool
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prompt "Power management"
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default n
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help
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This option enables the board to implement extra power management
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policies whenever the kernel becomes idle. The kernel informs the
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power management subsystem of the number of ticks until the next kernel
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timer is due to expire.
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if SYS_POWER_MANAGEMENT
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config SYS_POWER_LOW_POWER_STATE
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bool
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prompt "Low power state"
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default n
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depends on SYS_POWER_LOW_POWER_STATE_SUPPORTED
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help
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This option enables the kernel to interface with a power manager
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application. This permits the system to enter a custom CPU low power
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state when the kernel becomes idle. The low power state could be any of
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the CPU low power states supported by the processor. Generally the one
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saving most power.
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config SYS_POWER_DEEP_SLEEP
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bool
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prompt "Deep sleep state"
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default n
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depends on SYS_POWER_DEEP_SLEEP_SUPPORTED
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help
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This option enables the kernel to interface with a power manager
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application. This permits the system to enter a Deep sleep state
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supported by the SOC where the system clock is turned off while RAM is
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retained. This state would be entered when the kernel becomes idle for
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extended periods and would have a high wake latency. Resume would be
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from the reset vector same as cold boot. The interface allows
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restoration of states that were saved at the time of suspend.
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config DEVICE_POWER_MANAGEMENT
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bool
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prompt "Device power management"
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default n
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help
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This option enables the device power management interface. The
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interface consists of hook functions implemented by device drivers
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that get called by the power manager application when the system
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is going to suspend state or resuming from suspend state. This allows
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device drivers to do any necessary power management operations
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like turning off device clocks and peripherals. The device drivers
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may also save and restore states in these hook functions.
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config TICKLESS_IDLE
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bool
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prompt "Tickless idle"
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default y
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help
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This option suppresses periodic system clock interrupts whenever the
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kernel becomes idle. This permits the system to remain in a power
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saving state for extended periods without having to wake up to
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service each tick as it occurs.
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config TICKLESS_IDLE_THRESH
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int
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prompt "Tickless idle threshold"
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default 3
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depends on TICKLESS_IDLE
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help
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This option enables clock interrupt suppression when the kernel idles
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for only a short period of time. It specifies the minimum number of
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ticks that must occur before the next kernel timer expires in order
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for suppression to happen.
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config TICKLESS_KERNEL
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bool
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prompt "Tickless kernel"
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default n
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depends on TICKLESS_IDLE
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help
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This option enables a fully event driven kernel. Periodic system
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clock interrupt generation would be stopped at all times. This option
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requires Tickless Idle option to be enabled.
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config TICKLESS_KERNEL_TIME_UNIT_IN_MICRO_SECS
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int
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prompt "Tickless kernel time unit in micro seconds"
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default 1000
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depends on TICKLESS_KERNEL
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help
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This option makes the system clock and scheduling granurality.
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The default will be one mili second. This option also determines
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the time unit passed in functions like _sys_soc_suspend. The
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value should be determined based what the timer hardware and driver
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can support. Spceficying too small a time unit than what the overall
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system speed can support would cause scheduling errors.
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config BUSY_WAIT_USES_ALTERNATE_CLOCK
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bool
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prompt "Busy wait uses alternate clock in tickless kernel mode"
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default n
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help
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In tickless kernel mode, the system clock will be stopped when
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there are no timer events programmed. If the system clock is to
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be used to keep time e.g. to get a delata of time cycles then it
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needs to be turned on using provided APIs. Some platforms have
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alternate clocks which can be used instead. In that case this flag
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would be set to true. This flag would be checked before turning
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on the system clock in APIs that do busy wait reading clock
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cycles.
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endif
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