Messages in this thread | | | Date | Thu, 1 Apr 2004 11:50:02 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: finding out the value of HZ from userspace |
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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, Dick Johnson Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips). Note 96.31% of all statistics are fiction.
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