Question about cpu time accuracy.

Question about cpu time accuracy.

[Jennifer Huang]

Hi all,

I have a question about cpu time accuracy.

I am using kernel 2.4.18. But, when I tried "utime"
and "nanosleep" to get a process suspended, it only
worked in 10ms granularity, and it's no way to sleep
for 1 microsecond.

Anyone can help me out of this?
Thanks in advance,

-Jenny

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Re: Question about cpu time accuracy.

[Kurt Wall]

Scribbling feverishly on May 12, Jennifer Huang managed to emit:
> Hi all,
> 
> I have a question about cpu time accuracy.
> 
> I am using kernel 2.4.18. But, when I tried "utime"
> and "nanosleep" to get a process suspended, it only
> worked in 10ms granularity, and it's no way to sleep
> for 1 microsecond.

The standard kernel timer has a resolution of 1/HZ, which is 10ms on 
an x86. You could try a scheduling policy of SCHED_FIFO or SCHED_RR,
but this only gets you 2ms resolution. 

> Anyone can help me out of this?

There are patches available for high resolution timers:

http://sourceforge.net/projects/high-res-timers/
http://www.cs.wisc.edu/paradyn/libhrtime/

Kurt
-- 
Anarchy may not be the best form of government, but it's better than no
government at all.

Re: Question about cpu time accuracy.

[Jennifer Huang]

Thanks very much for your information.

Just one more question, does it work for 2.4.18?
Thanks.

--- Kurt Wall <kwall@kurtwerks.com> wrote:
> Scribbling feverishly on May 12, Jennifer Huang
> managed to emit:
> > Hi all,
> > 
> > I have a question about cpu time accuracy.
> > 
> > I am using kernel 2.4.18. But, when I tried
> "utime"
> > and "nanosleep" to get a process suspended, it
> only
> > worked in 10ms granularity, and it's no way to
> sleep
> > for 1 microsecond.
> 
> The standard kernel timer has a resolution of 1/HZ,
> which is 10ms on 
> an x86. You could try a scheduling policy of
> SCHED_FIFO or SCHED_RR,
> but this only gets you 2ms resolution. 
> 
> > Anyone can help me out of this?
> 
> There are patches available for high resolution
> timers:
> 
> http://sourceforge.net/projects/high-res-timers/
> http://www.cs.wisc.edu/paradyn/libhrtime/
> 
> Kurt
> -- 
> Anarchy may not be the best form of government, but
> it's better than no
> government at all.
> -
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Re: Question about cpu time accuracy. Er resolution!

[george anzinger]

Jennifer Huang wrote:
> 
> Thanks very much for your information.
> 
> Just one more question, does it work for 2.4.18?

Uh, thats what you are there for :)  Let me know what you find out.



-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Real time sched:  http://sourceforge.net/projects/rtsched/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml