On Wed, 22 Oct 2014, Joakim Hernberg wrote:
On Tue, 21 Oct 2014 14:05:23 -0700 (PDT)
Len Ovens <len@xxxxxxxxxxxxx> 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
www.ovenwerks.net
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