Messages in this thread | | | Date | Fri, 26 Mar 2004 10:22:09 +1100 | From | Peter Williams <> | Subject | Re: finding out the value of HZ from userspace |
| |
Jamie Lokier wrote: > Peter Williams wrote: > >>>Will this be USER_HZ or kernel HZ? >>>Someone earlier suggested it would be USER_HZ which would make it >>>pointless. >> >>It has to be whatever enables user space to correctly interpret values >>sent to user space as "ticks". That means USER_HZ and it's not useless >>as it enables USER_HZ to be different and/or change without breaking >>programs that use values expressed in "ticks". > > > It is, however, useless for the _other_ reasons userspace needs to > know kernel HZ, including as I mentioned userspace timer granularity.
Theoretically, which I know can be a pain, user space timer granularity should be in USER_HZ as, theoretically, this is the only one user space is supposed to know about. Because of this, in my view, HZ and USER_HZ should be the same or USER_HZ should be greater than HZ.
> > (Btw, that usage would be better as a period rather than a frequency, > so that a "tickless" kernel can report zero).
_SC_CLK_TCK is a POSIX.1 definition and can't be changed. But I don't think that there's any impediment to adding new parameters that can be reported by sysconf().
> > The fundamental problem is that there are two values, and both values > have programs which can usefully use them. > > How hard can it be to export both? >
Making HZ == USER_HZ would also solve the problem.
Peter -- Dr Peter Williams, Chief Scientist peterw@aurema.com Aurema Pty Limited Tel:+61 2 9698 2322 PO Box 305, Strawberry Hills NSW 2012, Australia Fax:+61 2 9699 9174 79 Myrtle Street, Chippendale NSW 2008, Australia http://www.aurema.com
- 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/
| |