Time.sleep(0.0125) not available within Linux

Grant Edwards grante at visi.com
Wed Oct 1 02:41:15 CEST 2008


On 2008-09-30, Michael Torrie <torriem at gmail.com> wrote:

>> Just a thought, your minimum sleep time is probably limited by
>> the resolution of the system "HZ" clock. Type
>> 
>>     less /proc/config.gz
>> 
>> and search for the value of the "CONFIG_HZ" setting. On the
>> Athlon 64 machine I'm using to write this, it's 250, which
>> should allow for sleep intervals in multiples of 0.004
>> seconds.
>
> Since most distributions do not create this file in /proc for whatever
> reason,

It's also common to put a copy of the config file in /boot (or
wherever the kernel binaries are installed).  I prefer the
/proc/config.gz setup myself, and that's how I configure all my
systems.

> and some people are being deliberately obtuse, does anyone
> know how to ask the kernel what the timer resolution is?  Is
> it stored anywhere else in /proc or /sys?  I kind of think
> most distros set it to 1000 Hz, but I'm not sure.

We could look in /usr/include:

   $ grep -r ' HZ ' /usr/include
   /usr/include/scsi/sg.h:#define SG_DEFAULT_TIMEOUT (60*HZ) /* HZ == 'jiffies in 1 second' */
   /usr/include/linux/ixjuser.h:* IXJCTL_HZ sets the value your Linux kernel uses for HZ as defined in
   /usr/include/linux/n_r3964.h: * Fixed HZ usage on 2.6 kernels
   /usr/include/asm/param.h:#define HZ 100

But, I happen to know that's wrong and I'm running a kernel with HZ=250.

So let's look elsewhere. How about in /proc/sys/kernel?

  $ cat /proc/sys/kernel/sched_min_granularity_ns 
  4000000

That looks suspiciously like 1/HZ in nanoseconds.

-- 
Grant



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