Re: finding out the value of HZ from userspace

From: Richard B. Johnson (root_at_chaos.analogic.com)
Date: 04/01/04

  • Next message: Jamie Lokier: "Re: 2.6 kernels misdetect harddisk geometry, 2.4 kernels are fine" 
    Date:	Thu, 1 Apr 2004 11:50:02 -0500 (EST)
To: Jamie Lokier <jamie@shareable.org>

    On Thu, 1 Apr 2004, Jamie Lokier wrote:

    > Arjan van de Ven wrote:
    > > HZ doesn't mean nothing, esp when we go to a tickless kernel...
    >
    > As explained several times in this thread, HZ is meaningful because it
    > affects the rounding in select/poll/epoll/setitimer. A few userspace
    > programs with low jitter soft-RT timing requirements need to
    > compensate for that rounding and/or deliberately synchronise
    > themselves with the tick.
    >
    > Such programs can determine HZ experimentally and lock onto the tick
    > in the manner of a PLL, but it would be nice to simply be able to
    > have the value, to reduce the number of control variables.
    >
    > When we go to a tickless kernel and offer high-resolution timers to
    > userspace, then it will be irrelevant. Until then, or if the kernel
    > goes tickless but limits the resolution of timers for efficiency, the
    > value of HZ is still relevant.
    >
    > Not to get irritatingly back to the subject of this thread or
    > anything, but... is the value of HZ reported to userspace anywhere?
    >
    > Thanks :)
    > -- Jamie

    I may be naive, but what's the matter with:

    #include <stdio.h>
    #include <sys/param.h> // Required to be here!
    int main()
    {
        printf("HZ=%d\n", HZ);
        return 0;
    }
    It works for me.

    Cheers,
    *** Johnson
    Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
                Note 96.31% of all statistics are fiction.

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

  • Next message: Jamie Lokier: "Re: 2.6 kernels misdetect harddisk geometry, 2.4 kernels are fine"