realtime:documentation:howto:tools:ticklesskernel
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realtime:documentation:howto:tools:ticklesskernel [2017/06/23 22:12] srodrig1 created |
realtime:documentation:howto:tools:ticklesskernel [2023/10/03 08:20] (current) costa.shul change title |
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| - | ====== Tickless Kernel ====== | + | ====== Dynticks or Tickless kernel or nohz ====== |
| - | Previously, the Linux kernel had by default a periodic interrupt that made the kernel scheduler to balance and schedule threads running among the CPU's, this interrupt is known as the timer tick and it was generated at a fix rate (usually in the order of hundreds/thousands per second), namely referred as HZ. | + | |
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| + | For a long time Linux kernel have a periodic interrupt that makes the kernel scheduler to balance and schedule threads running among the CPU's. | ||
| + | This interrupt is known as the **timer tick** and it is generated at a fixed rate 100-1000 HZ on each CPU or core. | ||
| The kernel serviced this interrupt regardless of the power state of the CPU. | The kernel serviced this interrupt regardless of the power state of the CPU. | ||
| + | This mode is enabled by option ''CONFIG_HZ_PERIODIC''. | ||
| + | |||
| + | ''CONFIG_NO_HZ_IDLE'' mode allows the CPU not to be disturbed when idle and can save power because it just wakes up the CPU when needed to service the timer. | ||
| - | Tickless kernel, or NO_HZ, is a configuration option in the kernel that allows it to run without a periodic timer tick. Running without a periodic timer tick allows the CPU not to be disturbed when idle and can save power because it just wakes up the CPU when needed to service the timer. | + | Full dynticks system (tickless) mode is enabled by ''CONFIG_NO_HZ_FULL'' and activated by [[https://docs.kernel.org/admin-guide/kernel-parameters.html#cpu-lists|nohz_full boot parameter]]. |
| + | The kernel adaptively tries to shutdown the tick whenever possible, even when the CPU is running tasks with function ''tick_nohz_full_cpu''. | ||
| - | The configuration option is CONFIG_NO_HZ and is set by Tickless System (Dynamic Ticks), on the Kernel Features configuration menu. | ||
| + | More information: | ||
| + | * [[https://www.suse.com/c/cpu-isolation-full-dynticks-part2/|CPU Isolation – Full dynticks internals]] | ||
| + | * [[https://en.wikipedia.org/wiki/Tickless_kernel|Tickless kernel]] | ||
| + | * [[https://docs.kernel.org/timers/no_hz.html|NO_HZ: Reducing Scheduling-Clock Ticks]] | ||
| + | * [[https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/Kconfig.hz|kernel/Kconfig.hz]] | ||
| + | * [[https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/time/Kconfig|kernel/time/Kconfig]] | ||
realtime/documentation/howto/tools/ticklesskernel.1498255928.txt.gz · Last modified: 2017/06/23 22:12 by srodrig1
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