[LAU] kernel rt-patches future

Len Ovens len at ovenwerks.net
Wed Oct 22 21:30:21 UTC 2014

On Wed, 22 Oct 2014, Joakim Hernberg wrote:

> On Tue, 21 Oct 2014 14:05:23 -0700 (PDT)
> Len Ovens <len at ovenwerks.net> wrote:
>> In my opinion, Much of the use for RT kernels in audio is to try and
>> fix problems with system HW tuning. In my trials, I have found that
>> using only a "lowlatency" kernel, I can get clean latency as low as
>> my card is able to be set anyway (32 samples). The only xruns I get
>> are from applications that do not shut down correctly or take to long
>> starting up (that is they enable ports in jack before they are
>> stable).
> IME/O, the one thing the -rt kernel brings to audio processing on
> linux is reliable kernel scheduling. Provided that all the hardware
> plays ball (which most does), you can expect a scheduling delay of
> under 100usecs with a -rt patched kernel.
> With vanilla kernels (even low latency ones), you can expect to see the
> occasional latency peak into the msec range, each such peak will mean
> an xrun if the kernel scheduling and audio processing latencies exceed
> the deadline as given by samplerate and buffer sizes.  They might be
> just occasional and not a problem, but they will be there.

I seem to be able to stress the cpu, use the desktop, and run jack at 16/2 
for hours on end with no xruns at all. Then load an app that uses jack and 
see xruns only while loading or exiting. sure, I don't do much synth work, 
more effects at that latency, but even still, I have been very impressed 
with just the low latency kernel. (i5 at 3.4G BTW) I think too, there are 
more switches in the kernel that can be un/set to make it more RT than the 
average lowlatency version.

I have not done that much system tuning either. I did choose the i5 on 
purpose for no HT, chose to use a pci AI and which slot it should be in. 
No wifi, performance mode. Mouse and kb are not USB (in fact no USB use at 
all, now that I think about it) Video is Intel based.

>> But yes, the standard RT keneral development is seeing the money dry
>> up.
> There never was any money to dry up.  Most of the development have been
> carried by https://www.linutronix.de, Red Hat and private individuals.

Red Hat was paying at least some people's salary and I think some of the 
companies who used RT allowed their employees to help out on company time 
as well (perhaps no official funding though).

Len Ovens

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