A tickless kernel is an operating system kernel in which timer interrupts do not occur at regular intervals, but are only delivered as required.^[1]

The Linux kernel on s390 from 2.6.6^[2] and on i386 from release 2.6.21^[3] can be configured to turn the timer tick off (tickless or dynamic tick) for idle CPUs using CONFIG_NO_HZ, and from 3.10 with CONFIG_NO_HZ_IDLE extended for non-idle processors with CONFIG_NO_HZ_FULL.^[4] The XNU kernel from Mac OS X 10.4 on, and the NT kernel from Windows 8 on, are also tickless.^[1] The Solaris 8 kernel introduced the cyclic subsystem which allows arbitrary resolution timers and tickless operation.^[5] FreeBSD 9 introduced a "dynamic tick mode" (aka tickless).^[6]

As of 2020, there is a plan to add this to MINIX 3^[7] in the medium term.^[8]

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