On Wed, 2005-04-27 at 09:13 +0100, Jamie Bullock wrote:

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

No I don't, I run it at 128 fpp, which is more like 6ms - still good though. You could probably get 64 with the edge kernel.

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.

Jamie

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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Mike,

On Wed, 2005-04-27 at 13:36 -0400, Mike Wozniewski wrote:

<snip> > By just the kernel, I meant I didn't want to install any of the > packages. We are building a pretty heavy application with Pd+Gem. We > already have a decently working system. But any extra performance we can > get out of our current machines is beneficial. The graphics end is quite > optimized - so now I'm focusing on audio. I was wondering what kind of > benefit CCRMA could give. It seems from the emails that it's more of a > convenience benefit than performance (ie, it's easier to download > packages, run -rt without being root, etc.)... If I can run pd as root > anyway, it's not going to benefit me that much right? AFAIK, the latency improvements are gained through improved scheduling. I.E., the preemption patch allows for one process to be pre-empted by another higher priority process. You can therefore make anything to do with audio have absolute priority on your system, and this improves latency etc. Unfortunately, this can be at the expense of other processes, and sometimes overall stability. If you want to run audio and real time graphics, you might end up optimising audio at the expense of graphics, and this would presumably be bad.

I hope this helps,

Jamie

I guess though, that latency is a bit different from performance. It sounds like the latency can be cut down a bit by CCRMA. Performance however - ie, CPU load - is unaffected right? Julien, you said that operating at lower latencies you get clicks when CPU load >80% ...does this mean that in fact low latency might hinder a heavily loaded application?

Thanks again for your responses, -Mike