Time.sleep(0.0125) not available within Linux

[Michael Torrie]

Re: Time.sleep(0.01 25) not available within Linux

Lawrence D'Oliveiro wrote:

In message <__KdneWJPotDx0 XVnZ2dnUVZ_gGdn Z2d@posted.usin ternet>, Grant
Edwards wrote:
>

>On 2008-09-23, Blubaugh, David A. <dblubaugh@belc an.comwrote:
>>

>>I was wondering if anyone has come across the issue of not being allowed
>>to have the following within a Python script operating under Linux:
>>>
>>time.sleep(0. 0125)

>No, I have not. And I doubt anybody else has.

>
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, 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.

[Grant Edwards]

Re: Time.sleep(0.01 25) not available within Linux

On 2008-09-30, Michael Torrie <torriem@gmail. comwrote:

>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_TIME OUT (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_granu larity_ns
4000000

That looks suspiciously like 1/HZ in nanoseconds.

--
Grant