[PD] benefits of planet ccrma kernel, and realtime priority pd?

Jamie Bullock jamie at postlude.co.uk
Wed Apr 27 10:13:05 CEST 2005

I don't have any scientific benchmarks, but FWIW, here is a bit of my
experience with CCRMA.

I have tried the stock FC3 kernel, built my own from vanilla sources +
patches and now I use only CCRMA. I don't know about RH9, but the only
significant difference between the stock FC3 kernel and the 'standard'
CCRMA kernel  is that CCRMA includes the LSM (Linux Security Module),
which allows non-root users to run applications with real time priority.
This is a convenience and not a performance enhancement. It also
introduces a security vulnerability, so it should be used with care if
your machine is on a LAN.

If you want serious a low latency, high performance system you need to
go for one of the Planetedge kernels, which include Ingo Molnar's
preemption patch. I don't use these, simply because I am happy with the
latency/performance of my system already. I run Jackd at 64 frames per
perid (2 periods per buffer), which gives a system latency of around 3
ms. I can do everything I need, but if I'm doing real time OpenGL with
Gem, and Audio, I down clock to 256 fpp, which is system latency of
around 11ms.

When you say just the kernel, do you mean the kernel and associated
modules? If you switch to the CCRMA kernel, you will need to get the
CCRMA ALSA drivers, and recompile any unique modules such as video
wireless network.

Also - you'll need root access to install the kernel unless you plan to
boot from a usb key or CD, in any case you'll be able to install the
apps as well, or am I missing something.


On Tue, 2005-04-26 at 19:13 -0400, Mike Wozniewski wrote:
> Hi.
> I asked a similar question about Gem a little while back, but now I'd 
> like to focus on audio alone.
> Has anyone ever published performance results/benchmarks when using the 
> Planet CCRMA kernel vs. a regular RedHat/Fedora kernel? Where can I find 
> them?
> ...or how about the benefit of using the -rt (realtime) option in Pd? I 
> don't seem to notice a difference.
> Is it worth it for me to install *just* the Planet CCRMA kernel for 
> RedHat 9? ...note that I can't really install anything else since I'm on 
> a networked machine with many restrictions. Will I get much improvement 
> from just the kernel alone?
> Also, is there a chance that the new kernel won't work with my existing 
> (alsa-enabled) RedHat9 system? or could it break something so that I 
> won't be able to return to my working system?
> Thanks,
> Mike Wozniewski
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