Subject: Re: [linux-audio-user] Re: Recent LKML discussion on preempt/latency in 2.6 kernels
From: Fernando Pablo Lopez-Lezcano (nando_AT_ccrma.stanford.edu)
Date: Thu Mar 25 2004 - 23:31:45 EET
On Thu, 2004-03-25 at 13:05, Steve Harris wrote:
> On Thu, Mar 25, 2004 at 11:35:26AM -0800, Fernando Pablo Lopez-Lezcano wrote:
> > I was adding:
> > realtime security module (LSM) 0.0.4
> > http://www.joq.us/realtime
> > low latency scheduling additions by Takashi Iwai
> > http://kerneltrap.org/node/view/2702
> > drm scheduling additions (radeon/mga/r128) --> broken!
>
> What kind of latency were you getting with this, compared to patched 2.4?
Reposting:
a) preempt enabled, Takashi's patches included, x11 sucks...
http://www-ccrma.stanford.edu/~nando/latencytest/20040323/2.6.4-1.279.ll.ccrma/
b) preempt enabled, added tweaked radeon low latency patch, much better:
http://www-ccrma.stanford.edu/~nando/latencytest/20040323/2.6.4-1.279.ll.ccrma.radeon/
c) preempt disabled, with Takashi's and radeon patches:
http://www-ccrma.stanford.edu/~nando/latencytest/20040323/2.6.4-1.286.1.ll.radeon/
d) same as c), with preempt enabled again:
http://www-ccrma.stanford.edu/~nando/latencytest/20040323/2.6.4-1.286.2.ll/
e) same as d), without loading the xfree86 dri module:
http://www-ccrma.stanford.edu/~nando/latencytest/20040323/2.6.4-1.286.2.ll.nodri/
This is from the output of latencytest 0.52 and looks very good. But,
and it is not a small but, when I tried to use real jack and jack
applications I could not go down to 2x128 at all, kept getting small
xruns. But an idle jack at 2x64 plus disk activity ("tar cf usr.tar
/usr") would very seldom generate xruns.
So there is something else that needs tweaking[*].
Takashi's patches do improve the situation quite a lot.
-- Fernando
[*] plus my setup was not really that stable. For some reason depending
on how I had the hwconf setup done by kudzu (or not) I would get into
situations where moving the mouse was creating all sorts of small xruns
in an otherwise idle jack. That drove me nuts for the better part of a
day, where I could not get back to the nice "almost no xrun" situation
although I thought I was "undoing" everything I had done.
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