[music-dsp] Pre-emptive kernel for DSP

[Jamie Bullock]

Hi,

I'm not an expert either, but my understanding is that the 'low latency 
patch' and the 'preemption patch' were two distinct ways of fudging an 
improvement in scheduler performance with the 2.4 kernel. As I 
understand it, CCRMA and Agnula are still distributing (and using?) a 
patched 2.4 kernel, but also releasing RPMs for Fedora Core 1/2 (2.6 
kernel) for those who want them.

My understanding is that 2.6.x kernels do not require a 'low latency 
patch', as latency is already drastically improved compared to an 
un-patched 2.4 kernel. However, whilst pre-emption is offered as a 
compile time option, it is not enabled by default in the pre-compiled 
kernel shipped with the distro'. Hence my question. There must be good 
reasons why it is not enabled by default, and I don't want to do a 
kernel recompile unless there is decent performance enhancement...

Jamie

mdsp wrote:

> hi,
>
> I'm not an expert.
>
> AFAIK linux standard kernel is not preemptive, but when installing 
> planetCCRMA over RedHat/Fedora you patch it to be preemptive.
> I think that AGNULA DeMuDi and RehMudi comes with an already patched 
> kernel.
> And BSD unices have a premptive kernel by default, thus macOSX 
> mini-kernel is preemptive.
>
> maybe I'm wrong.
>
> cheers
>
> remy
>
>
> Payan, Remi wrote:
>
>> Hi Jamie,
>> I'm quite interested in this topic, but I did not know Linux was not
>> preemptive by default.
>> My understanding is as follows.
>> Preemptive means: at any time, the current thread executing is the one
>> with the highest priority and that is ready to execute. It implies
>> thread switching is asynchronous and can happen at any time.
>> A non-preemptive scheduler only switches at regular time intervals
>> (ticks).
>>
>> I believe most real-time kernels are preemptive (like TI's DSP/BIOS and
>> ENEA's OSE, for those I know of).
>>  
>> Do you know where to find information on this feature of the Linux
>> kernel?
>>
>> Thanks,
>> Remi
>>
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