Messages in this thread |  | | | Date | Wed, 25 Jun 2008 09:09:39 +0200 (CEST) | | From | Thomas Gleixner <> | | Subject | Re: When did High-Resolution Timers hit mainline? |
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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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