Rt kernel very makes system very slow

Hi all,
I’m relatively noob with linux/Ardour. I have managed to get Ardour and Edirol UA-25 work with very low latensy and no xruns. The problem is with RT-kernel. The top says IRQ-20 is eating 44.5% of processor’s power. The system is very slow compared with non rt-kernel. Here are the interrups.


0: 556 IO-APIC-edge timer
1: 172 IO-APIC-edge i8042
8: 7 IO-APIC-edge rtc
9: 450 IO-APIC-fasteoi acpi
12: 592 IO-APIC-edge i8042
14: 10926 IO-APIC-edge ide0
15: 5364 IO-APIC-edge ide1
16: 2991 IO-APIC-fasteoi uhci_hcd:usb1, ehci_hcd:usb2, uhci_hcd:usb3, uhci_hcd:usb4
17: 349 IO-APIC-fasteoi eth0
19: 184 IO-APIC-fasteoi VIA82XX-MODEM, VIA8233
20: 31343424 IO-APIC-fasteoi via@pci:0000:01:00.0
NMI: 0
LOC: 324202
ERR: 0
MIS: 0

Any ideas?

yeah, its a VIA. as noted here: http://ardour.org/system_requirements
you want to avoid VIA hardware like the plague if low latency matters to you.


do you really need an -rt kernel?
I used to use one, too, but I also had a few glitches and realized that I don’t really need the -rt kernel. It’s only important for low latency which is then again only important for software monitoring while recording in my understanding.

Plus I can get down to 128 frames with the normal kernel without problems.

Btw, do you have a VIA chipset?


Ok, it seems that the VIA is to blame, which is a pity because the laptop was pretty cheap and my other experiences with linux/kubuntu have been so positive.

Benjamin, the -rt kernel gave better latency figures than the normal kernel despite the slowness of system.
Yes, the latency needs to be tight when doing overdubs against previous recordings

I may still need to do some serious tweaking.
Should I use an external disk for audio as I do in my XP system?
Ideas welcome.


An external disk for audio will help a lot. Firewire will work much better than USB, just on the interface, regardless of the actual drive. An IDE drive in a cheap external case with Firewire interface will perform much better than a USB connection.

Correct me if I’m wrong please Paul, but doesn’t ardour compensate for latency, so overdubs are in sync? I remember being told this by a developer…in other words it doesn’t matter how large the latency ardour will compensate so that the recorded material is delayed to match the latency of the realtime overdubbing.
For this reason, a realtime kernel is only really essential for other applications such as live performances with DSP on the instruments?

If I’m right…is there a way this can go in the installation/setup instructions or something…because so many people bust their balls to get better latency…and if they don’t even need to bother then a lot of people are worrying for no reason.


yes, Ardour compensates the latency.
Therefore overdubs are no problem at any latency - except if you’re using software monitoring. There the latency should be around 3ms or less I’d say.
If you’re using zero latency hardware monitoring (most semi-pro audio cards support this), you’ve got no problem with latency within Ardour. But software monitoring is sometimes nicer for me, so there it would matter.

To conclude, the Ardour (more precise jack) latency matters when you’re doing live performance through Ardour or software monitoring.

A hint to every user would be great, yes.

Corrections are crucial if I’m wrong here.