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SubjectRe: When did High-Resolution Timers hit mainline?
On Wed, 25 Jun 2008, Michael Kerrisk wrote:
> High-Resolution Timers
> Before Linux 2.6.16, the accuracy of timer and sleep system
> calls (see below) was also limited by the size of the jiffy.
> Since Linux 2.6.16, Linux supports high-resolution timers
> (HRTs), optionally configurable since kernel 2.6.21 via CON-
> FIG_HIGH_RES_TIMERS. On a system that supports HRTs, the accu-
> racy of sleep and timer system calls is no longer constrained
> by the jiffy, but instead can be as accurate as the hardware
> allows (microsecond accuracy is typical of modern hardware).

Hmm, that's a bit backwards. We changed the internal handling of those
interfaces to hrtimers in 2.6.16, but the accuracy is still jiffies
unless you have CONFIG_HIGH_RES_TIMERS enabled (which is only possible
as of 2.6.21) and your system provides the necessary hardware.

> HRTs are not supported on all hardware architectures. (Support
> is provided on x86, arm, and powerpc, among others.)

Also you might point out that you can check whether high resolution
timers are active via clock_getres() or by checking the resolution
entry in /proc/timer_list.



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