[LAD] cpu spikes

Jonathan E. Brickman jeb at ponderworthy.com
Thu Jan 28 13:37:47 UTC 2016

First of all, for the record, anyone who equates firsthand experiences 
with snakeoil, shall find their words completely ignored by yours truly :-)
> First of all, booting into console mode, rather than running the full 
> blown desktop seemed to eliminate most of the problems, although it’s 
> still not quite a stable as i’d like.
> Also i don’t quite understand how all of that could interfere with my 
> RT-thread.
> This was going to try and install a more minimal system anyway, and 
> don’t need a graphical environment for this, but during developments 
> it’s kind of nice to have.
Check your processes with htop.  Make sure none of the resources-eating 
background items remain.
> I still would like to see how far i can take this, and was really 
> hoping i can continuously use 80-90% of all cpu cores without dropouts…
> Is that realistic with a lowlatency kernel?
In my experiences this is not realistic with either a realtime kernel or 
a lowlatency kernel, unless you can afford large latency times, using 
large audio buffers.  This is because in a low latency situation, the 
CPU has to have a lot of free cycles available to be ready to handle 
everything which comes.

I do think you will probably see more stability if you use JACK in such 
efforts, or even PulseAudio, than if you use direct ALSA.  I have found 
ALSA to be great for drivers, not anywhere near so good for the 
transport phases.
>> Cron should also be turned off, but that is probably not the problem 
>> here. Cron runs super "nice" but there seem to be some things it does 
>> like packge update that can cause problems too. I turn off cron while 
>> recording.
I have never had to turn cron on an otherwise well-approached environment.
> I don’t have a wireless on my machine, nor an nvidia card. just intel 
> builtin graphics. This where my linux knowledge falls short, but If i 
> don’t have that hardware, can I assume no drivers for it are loaded?
Yep, no problem there.
>> AFAIK, the important things are.
>> 1. Use a properly configured realtime patched kernel.
> lowlatency-kernel is not going to cut it?
Lowlatency is just fine if you have the CPU for it, and lowlatency is a 
whole lot easier to set up now, with the Liquorix people on the ball 
like they are.
> I wasn’t really able to find to much info on the difference between 
> the two, other than than the rt-kernel is a “step up” and hard 
> realtime vs soft.
> But nothing on how this is technically achieved
On my production box, with my Behringer Firewire FCA202, I have found 
slightly better results using a Liquorix kernel than with a 
realtime-patched kernel.  Liquorix has a whole lot of interesting 
optimizations.  I would imagine that if my CPU were not what it is, 
and/or the load type different, the differences would probably be 
considerably greater, and I have no thought as to which side it would 
land on.

Jonathan E. Brickman   jeb at ponderworthy.com   (785)233-9977
Hear us at http://ponderworthy.com -- CDs and MP3 now available! 
Music of compassion; fire, and life!!!
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