Subject: Re: [linux-audio-dev] kernel preemption patch to 2.5 kernel tree!
From: Andrew Morton (akpm_AT_zip.com.au)
Date: Mon Feb 11 2002 - 11:11:07 EET
Kai Vehmanen wrote:
>
> This is great news. Linus has now added Robert Love's kernel preemption
> patch to the 2.5 tree!
>
> http://www.linuxdevices.com/news/NS3989618385.html
>
> --cut--
> "The addition of kernel preemption to the 2.5 tree is a substantial
> feature which will provide benefit to a range of uses," Love told
> LinuxDevices.com.
Alas, Robert protesteth too much.
As I'm sure those on this list have noticed (I've only rejoined recently),
the preemptive kernel is basically useless at this time. Worst-case
latencies are still in the 50-100 millisecond range, and the average
is only moderately improved. The comments and reactions in the
popular press are pretty amazing to someone who has actually performed
the measurements, trust me.
I recommended to Linus that the preemptive kernel patch be merged,
because it provides a sane basis upon which to start working on the
*hard* parts of providing good latencies from the kernel. That
work hasn't started yet. Probably a lot of it will come from
myself. So you can expect kernel 2.6 to be useful for the applications
which people on this list are interested in.
But 2.6 is some time away. Maybe years. At this time the only
solutions are a patched kernel with the low-latency patch, or the
preempt patch and the "lock-break" patch, which is a low-latency
derivative.
There is hope - at present, RedHat's rawhide kernel, at
ftp://ftp.redhat.com/pub/redhat/linux/rawhide/i386/RedHat/RPMS/
contains the full-on low-latency patch. Whether that is
permanent I do not know.
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