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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.

    Thanks,

    tglx



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