Kernels for low latency/real time environments

[Sean McNamara]

Hi,

On Fri, Mar 12, 2010 at 7:42 AM, Alessio Igor Bogani <abogani at ubuntu.com> wrote:
> Hi All,
>
> For those who are interested I have placed two new kernels
> (-lowlatency and -realtime) into my PPA:
> https://launchpad.net/~abogani/+archive/ppa
>
> The -lowlatency kernel contains a more aggressive configuration to
> reduce latency than the -preempt one. But like -preempt it doesn't
> contain any code changes (so both start from the same -generic source
> tree).

Do you offer any low latency setups that do not use the fully
preemptible kernel option?

As of Catalyst 10.2, the fglrx proprietary ATI kernel module will
"BUG" out on a fully preemptible kernel under certain circumstances.
Of course, it is ATI's fault that their driver is not designed to
handle a fully preemptible kernel, but it does work with voluntary
preemption.

I realize that full preemption is a very significant step towards
lower latency for things like audio, but are there any alternative
configurations that can result in some degree of lower latency on
systems that are forced to use fglrx for a decent experience (e.g.
Radeon HD5000 series)?

Thanks,

Sean

>
> The -realtime kernel contains the upstream version of PREEMPT_RT
> patchset applied to a vanilla Linux kernel. The Ubuntu Archive already
> provides the linux-rt package but it uses the Karmic source tree as
> base for PREEMPT_RT patchset.
>
> The PPA also contains meta-packages so that after you have added PPA
> into your Ubuntu system a simple "sudo apt-get install linux-realtime"
> or "sudo apt-get install linux-lowlatency" will install what you need.
> There is also a recent copy of rt-tests for evaluation and comparison
> of all kernels and to better identify which meets your needs.
>
> I suggest following these simple rules:
>
> *) if you don't need a low latency system use -generic kernel
> *) If you need a low latency system please use -preempt kernel as a
> first choice (this reduces latency but doesn't sacrifice power saving
> features) from the Ubuntu archives directly from Ubuntu Kernel Team
> *) If you have an i386 system or -preempt isn't enough for your needs
> you should try the -lowlatency kernel present in my above-mentioned
> PPA.
> *) If -lowlatency also isn't enough you should try the -realtime
> kernel (like -lowlatency it is available through my PPA)
>
> Feel free to get in touch with me if you find these useful.
>
> Thanks!
>
> Ciao,
> Alessio
>
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