[PlanetCCRMA] Reliable version of Fedora using rt-kernel?

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Mon Nov 14 10:57:17 PST 2011

On 11/13/2011 11:09 PM, mark wrote:
> Hello,
> as far as i know the Kernel is already RT patched.

No, that is incorrect.

Parts of the rt patch set migrated to mainline in the 2.6.39.x cycle, 
most importantly threaded irqs, but 2.6.39.x definitely does not have 
all of the rt patch. Not only the kernel has to be built with the right 
options but you have to include a kernel boot line parameter to activate 
threaded irqs.

The only (current) kernel versions to have rt patches available are 
2.6.33.x, 3.0.x and 3.2-rc1. The 3.1 kernel series will not have an rt 

>I have tried
> to compile Kernel 3 with patch at debian 6 but it didn`t to run better.
> The latency was worse than without the patch. Anyway don`t forget to
> input those two lines for jackd into the limits.conf and add your user
> to the desired group.
> i would suggest to use either Kernel or just Ubuntu Studio
> 11.04 (not 11.10!!!).

As this list is about Planet CCRMA running on Fedora I would instead 
suggest Fedora 14 and 2.6.33.x :-)

So, the most tested, reliable and best performing rt kernel currently is 
2.6.33.x and that means Fedora 14 at most (the default startup system in 
15/16 needs newer versions of the kernel). Next down is 3.0.9-rt25 which 
could be used in Fedora 15 or 16. Next is the default Fedora kernel.

-- Fernando

> On 14.11.2011 00:23, Fernando Lopez-Lezcano wrote:
>> On 11/13/2011 12:05 PM, John S. Dey wrote:
>>> Hi Fernando,
>>> Thanks for getting back to me. No. You're presumption was incorrect. I
>>> hadn't install rtirq. I have now but it didn't make much different.
>> (it does not necessarily make a difference, basically it tries to give
>> better priority to the soundcard hardware interrupts, to test you have
>> to reboot or - as root - do a "/sbin/service rtirq start" from a
>> terminal... just in case you did not)
>> -- Fernando
>>> On Nov 12, 2011, at 9:17 PM, Fernando Lopez-Lezcano wrote:
>>>> On 11/12/2011 02:06 PM, John S. Dey wrote:
>>>>> Hi,
>>>>> I'm currently using 3.0.7-1.rt20.1.fc15.ccrma.x86_64.rt as my kernel
>>>>> on fc15 running on a thinkpad T60p with ATI graphics. I haven't been
>>>>> able to find settings for jackd that produce reliable real time
>>>>> performance. In the past I could achieve latency as presented in
>>>>> qjackctl of less than 10ms. Now I get xruns with latencies of 40ms
>>>>> and more. The stock kernel is just as good.
>>>> What soundcard do you have and what parameters did you use for jack?
>>>> (just curious).
>>> cat /proc/asound/cards
>>> 0 [Intel ]: HDA-Intel - HDA Intel
>>> HDA Intel at 0xee400000 irq 49
>>> 1 [Set ]: USB-Audio - C-Media USB Headphone Set
>>> C-Media USB Headphone Set at usb-0000:00:1d.0-2, full speed
>>> 29 [ThinkPadEC ]: ThinkPad EC - ThinkPad Console Audio Control
>>> ThinkPad Console Audio Control at EC reg 0x30, fw 79HT50WW-1.07
>>> I have varied Frames/Period and Periods/Buffer (2,3 and 4) but haven't
>>> been able to get
>>> stable results better that what is shown. I ran with both sound cards
>>> shown above. The rt kernel wasn't any better that the up to date stock
>>> kernel.
>>> Thanks,
>>> John
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