[LAU] Re: difference between realtime-kernel and low-latency-kernel?

[Kjetil S. Matheussen]

Florian Schmidt:
>> Generally we have two kinds of kernels: The "vanilla" kernel as
>> downloadable on kernel.org and the same kernel, but patched with Ingo
>> Molnars RT-patches. The vanilla kernel, if configured properly with
>> CONFIG_PREEMPT etc., already gives very good performance in the low
>> latency department, enough for many users, even audio users. I run one
>> of these.
>
> Well, the vanilla kernel also has a CONFIG_HZ setting of i think 200hz per
> default. This is too little timing resolution for processes that rely on the
> system timer frequency being higher [some sequencers come to mind]..
>
> The "lowlatency" kernel in ubuntu thus has CONFIG_HZ set to 1000 and
> CONFIG_PREEMPT enabled.
>

You don't need a lowlatency kernel to be able to set CONFIG_HZ to 1000. 
Its just the default value in vanilla which is 250Hz, but you can set it 
to 1000 if you want to.



> This might be good enough for some people..
>
> For a truly reliable system (where you can count on no audio period being
> missed because you forgot to disable the damn updatedb cronjob) you need a
> system patched with ingo's realtime preemption patches and have it properly
> configured.

Hasn't this been fixed a long time ago? Its true that you were required to 
have a realtime kernel when using linux 2.4 to avoid dropouts for cronjobs 
etc., and in practice you probably also couldn't get reliable realtime 
performance with old versions of 2.6. But I thought it shouldn't be like 
that anymore? At least I haven't had any dropouts with my vanilla 2.6 
kernel as long as I've used it.