[Fedora-music-list] Low Latency vs. Real Time Kernel - actual latencies ?

[Brian Monroe]

I didn't have time tonight to get tests on all the kernels under load, but
here are the results, relatively load free.

I need to write a short python program to put the systems under duress.
Hopefully I'll have time tommorrow to work on it and I can have the rest of
the results in.

PS:I'm attaching some results from an RT kernel on a debian system below
that they used while the box was recieving flood ping from an external
source and repeated loops of hackbench 25 and ls -Ral /.

# cyclictest -a -t -n -p99 -i100 -d50
560.44 586.11 606.12 211/1160 3727
T: 0 (18617) P:99 I:100 C:1011846111 Min:  2 Act:  4 Avg:  5 Max: 39
T: 1 (18618) P:98 I:150 C: 708641019 Min:  2 Act:  5 Avg: 11 Max: 57



On Thu, Feb 16, 2012 at 10:37 AM, Fernando Lopez-Lezcano <
nando at ccrma.stanford.edu> wrote:

> On 02/16/2012 04:33 AM, David Timms wrote:
>
>> On 15/02/12 16:49, Brian Monroe wrote:
>>
>>> On Tue, Feb 14, 2012 at 12:21 PM, Brendan Jones
>>> <brendan.jones.it at gmail.com>**wrote:
>>>
>>>> Latency times are really relative things based on many factors. Have you
>>>> been getting better latency times than ta
>>>>
>>>>  yeah.
>>>
>>
>> I would be good to see real numbers associated with claims like the
>> above; also how it is measured..
>>
>
> Cyclictest is widely used for measuring latencies:
>  https://rt.wiki.kernel.org/**articles/c/y/c/Cyclictest.html<https://rt.wiki.kernel.org/articles/c/y/c/Cyclictest.html>
>
>
>  Also, indicate those various kernel patches and or options they use or
>> have tested.
>>
>
> The rt patches for the latest kernels (3.2 at this point) are here:
>  http://www.kernel.org/pub/**linux/kernel/projects/rt/3.2/<http://www.kernel.org/pub/linux/kernel/projects/rt/3.2/>
>
> This is pretty much all I add to the rt patched kernels for Fedora (with
> the proper configuration options, of course, I'm attaching the extra
> options I'm currently using). To get the best performance in the Jack world
> you need to tune the irq kernel thread priorities, that is usually done
> using rtirq (http://www.rncbc.org/jack/#**rtirq<http://www.rncbc.org/jack/#rtirq>),
> and of course jackd should run with the proper rt priority as well.
>
> -- Fernando
>
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