3 Oct
2007
3 Oct
'07
8:46 p.m.
Florian Schmidt:
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.
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.
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.