Den sön 7 juni 2020 kl 13:22 skrev rosea.grammostola <rosea.grammostola@xxxxxxxxx>:
On 6/4/20 3:09 PM, Paul Davis wrote:
This is wrong. The behavior of a "normal", "low latency" and "preempt-RT" kernel are all different, and for realtime audio work, the correct behavior is only going to happen with a "preempt-RT" kernel.
However ...
The behavior of the normal and "low latency" kernels have changed over the years too, and on *some* systems (from a hardware perspective), they will function similarly enough to a "preempt-RT" kernel that a realtime audio workflow will be just fine. In addition, the "behavior" gap between a "preempt-RT" kernel and a normal kernel will be less and less apparent as the latency settings (buffer/period size) become more relaxed (i.e. grow larger).
How do you know which systems this is true for? You just have to try it. It is a complicated mixture of many different aspects of the hardware. There's an overview of the kinds of things that can contribute to the need for a "preempt-RT" kernel here:
Useful information.
Fwiw, I did my best to optimize a thinkpad t420 laptop for linuxaudio using the realtime script from the wiki mostly and the information in the Ardour docs.
Hey I got one of those, very good laptop :)
At least I can run Zynaddsubfx with 0.726 msec latency now without xruns using a cheap Behringer usb device. ;)
Do you mind sharing a bit more what settings and toolchain this includes?
kernel? distro? Jack? what buffersettings?
--
On a related note, I tested some more with the standard xanmod-rt-edge kernel on another laptop (hp something, the troubled one I mentioned earlier) under kubuntu 20.04 and it does seem this kernel behaves a bit better than the lowlatency kernel I had before. It is not a night and day difference.
Also, not sure if this is general knowledge, but I've had the feeling before that disabling graphical login and running X with startx improves resiliency to xruns, tried it now again and I believe it is still true.
I've got no metrics apart from counting xruns when doing some startup operations of my rig with 128 frame buffers.
/Robert
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