High-resolution user/system times?

[Orna Agmon Ben-Yehuda]

Reminder from years back: we would love to have a Haifux talk about timers,
time, tickless kernel, Jiffies, etc.
So if you (that's you) are reading this, and are interested in the topic,
what is a better time to learn it to depth and talk about it?

Thanks
Orna

On Wed, Jul 25, 2012 at 3:28 PM, Oleg Goldshmidt <pub at goldshmidt.org> wrote:

>
>
> On Wed, Jul 25, 2012 at 2:29 PM, Nadav Har'El <nyh at math.technion.ac.il>wrote:
>
>>
>> HZ used to default to 100 in the Linux kernel, but now it actually
>> defaults (unless I'm mis-remembering) to 250, and this is where the 4-ms
>> resolution came from.
>
>
> Actually, there is the default HZ and inside the kernel HZ there is HZ
> that you can configure at compile time (with CONFIG_HZ) and USER_HZ, which,
> I think, is still 100 whether or not the kernel's HZ is customized. I think
> USER_HZ is what is important for "soft timers" you are interested in.
>
> Unless you configure the kernel yourself, the HZ value the kernel comes
> with probably depends on the distro. The tradeoff is as follows: desktop
> systems benefit from a higher HZ value because interactive processes are
> latency-sensitive. Servers, especially NUMA systems, don't have interactive
> processes and may, on the other hand, experience a lot of unpleasant
> effects (bus contention as an example) if there are lots of interrupts.
> Also note that the interrupt rate will be HZ*#CPUs.
>
> I am used to RedHat systems whose kernels normally come with HZ=100. You
> are talking about a server as well, right? You may be right about HZ=250 by
> default in the vanilla kernel that is supposed to be a compromise between
> 100 and 1000.
>
> If you go back to, say, 2.6.11 or 2.6.12, then you'll see HZ=1000 by
> default, I think. Was that "Linux on a desktop"? ;-)
>
>
> --
> Oleg Goldshmidt | oleg at goldshmidt.org
>
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> Linux-il at cs.huji.ac.il
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>
>


-- 
Orna Agmon Ben-Yehuda.
http://ladypine.org
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