2 Nov
2003
2 Nov
'03
7:41 a.m.
Hi.
I'm confused about whether or not I have a low-latency kernel, and if not why
not. I installed the multimedia kernel and booted into it but:
[root@olaf joe]# cat /proc/version
Linux version 2.4.22-21mm.1mdk (dtholen(a)klama.mandrake.org) (gcc version 3.3.1
(Mandrake Linux 9.2 3.3.1-4mdk)) #1 Tue Oct 28 15:05:18 CET 2003
[root@olaf joe]# cat /proc/sys/kernel/lowlatency
cat: /proc/sys/kernel/lowlatency: No such file or directory
Does this definitely mean I don't have low-latency? Any ideas why not? Can't
identify anything relevant in /var/log/messages.
Does /proc/sys/kernel/lowlatency relate to the pre-emption patches or Andrew
Morton's low-latency patches or both or what?
Thanks for any help.
2 Nov
2 Nov
8:10 a.m.
On Sun, 2 Nov 2003 11:41:57 +0000
Joe Button <linux-audio-user(a)joebutton.co.uk> wrote:
Does /proc/sys/kernel/lowlatency relate to the
pre-emption patches or
Andrew Morton's low-latency patches or both or what?
It definetly relates to the low-level patches. I first compiled a kernel
with LL patches only. The patch creates a ioctl in
/proc/sys/kernel/lowlatency
which can be used as documented.
I have the preemptable patches installed now, too. I don't knwo how to
control these though.. The capabilities you can check by installing
liubcap and reconfiguring then recompiling jackd. the use your usual
jackd -R .. line with s/jackd/jackstart.
Florian Schmidt
8:41 a.m.
On Sun, 2 Nov 2003 13:16:25 +0100
Florian Schmidt <mista.tapas(a)gmx.net> wrote:
It definetly relates to the low-level patches. I first
compiled a
kernel with LL patches only. The patch creates a ioctl in
/proc/sys/kernel/lowlatency
Of course. like Robert Jonsson said, this happens only when the ioctl
interface is enabled in the kernel config. So if it is not enabled i
don't know how to find out..
Florian Schmidt
8:20 a.m.
söndagen den 2 november 2003 12.41 skrev Joe Button:
Hi.
I'm confused about whether or not I have a low-latency kernel, and if not
why not. I installed the multimedia kernel and booted into it but:
[root@olaf joe]# cat /proc/version
Linux version 2.4.22-21mm.1mdk (dtholen(a)klama.mandrake.org) (gcc version
3.3.1 (Mandrake Linux 9.2 3.3.1-4mdk)) #1 Tue Oct 28 15:05:18 CET 2003
[root@olaf joe]# cat /proc/sys/kernel/lowlatency
cat: /proc/sys/kernel/lowlatency: No such file or directory
I'm not sure exactly which patches the mm kernel has, but it most definitely
has the lowlatency patch and I'm pretty sure it's got the preemtion patch
aswell.
That you are missing the /proc/sys/kernel/lowlatency doesn't mean anything. It
is selectable in the kernel configuration whether it should show up.
It is related to the lowlatency patch btw.
/Robert
Does this definitely mean I don't have low-latency? Any ideas why not?
Can't identify anything relevant in /var/log/messages.
Does /proc/sys/kernel/lowlatency relate to the pre-emption patches or
Andrew Morton's low-latency patches or both or what?
Thanks for any help.
12:01 p.m.
Hi,
All Mandrake mm kernels have at least the low latency and pre-emption
patch, and the version you are running (2.4.22-21mdk) also has the
sched(0) patch.
Austin
--
Austin Acton
Synthetic Organic Chemist, Teaching Assistant, Ph.D. Candidate
Department of Chemistry, York University, Toronto
MandrakeLinux Volunteer Developer, homepage: www.groundstate.ca
5:04 p.m.
I thought that _ought_ to be the case but I was suspicious because of the
/proc/sys/kernel/lowlatency thing and also because I get very noticeable
audio dropouts when I do things like task-switch. jackd doesn't report xruns
though.
Am I correct in thinking that if I start jackd as root I don't need to use -R
or jackstart or anything to get good performance? At the moment I think I'm
using jackd -d alsa -d hw:0 -p 512 (although that's in a script on my other
PC so I might be mis-remembering).
Cheers.
On Sunday 02 November 2003 4:01 pm, Austin wrote:
Hi,
All Mandrake mm kernels have at least the low latency and pre-emption
patch, and the version you are running (2.4.22-21mdk) also has the
sched(0) patch.
Austin
5:25 p.m.
söndagen den 2 november 2003 17.40 skrev Joe Button:
I thought that _ought_ to be the case but I was
suspicious because of the
/proc/sys/kernel/lowlatency thing and also because I get very noticeable
audio dropouts when I do things like task-switch. jackd doesn't report
xruns though.
Am I correct in thinking that if I start jackd as root I don't need to use
-R or jackstart or anything to get good performance? At the moment I think
I'm using jackd -d alsa -d hw:0 -p 512 (although that's in a script on my
other PC so I might be mis-remembering).
No, it's the other way around. -R is only available when you run as root, or
with "root capabilities".
It is not possible to get good performance without running with -R.
/Robert
Cheers.
On Sunday 02 November 2003 4:01 pm, Austin wrote:
> Hi,
> All Mandrake mm kernels have at least the low latency and pre-emption
> patch, and the version you are running (2.4.22-21mdk) also has the
> sched(0) patch.
>
> Austin
7:08 p.m.
On Sun, 2003-11-02 at 11:40, Joe Button wrote:
I thought that _ought_ to be the case but I was
suspicious because of the
/proc/sys/kernel/lowlatency thing
Yeah, I dunno why Danny made it that way. I think just to make sure
lowlat was enabled by default with that kernel.
and also because I get very noticeable
audio dropouts when I do things like task-switch. jackd doesn't report xruns
though.
The #1 best thing you can do is mount /tmp as tmpfs. See the jack
homepage. It makes all the difference. Also, if you are using KDE,
Mandrake has this stupid idea of renicing X to -10, which makes the mm
kernel very stop-and-go. Adjust the -n level to 0 in
/etc/X11/xdm/Xservers. If you're using gdm (as all sane people do), you
don't have to worry, X is not reniced by gdm.
Am I correct in thinking that if I start jackd as root
I don't need to use -R
or jackstart or anything to get good performance? At the moment I think I'm
using jackd -d alsa -d hw:0 -p 512 (although that's in a script on my other
PC so I might be mis-remembering).
With the mm kernel, you should install jack-realtime, and start jack as
a normal user with 'jackstart'. That's part of the mm kernel's purpose.
Try using qjackctl too. It lets you adjust all the jack parameters and
compare the performance.
Austin
--
Austin Acton
Synthetic Organic Chemist, Teaching Assistant, Ph.D. Candidate
Department of Chemistry, York University, Toronto
MandrakeLinux Volunteer Developer, homepage: www.groundstate.ca
3 Nov
3 Nov
6:36 a.m.
Also, if you are using KDE,
Mandrake has this stupid idea of renicing X to -10, which makes the
mm kernel very stop-and-go. Adjust the -n level to 0 in
/etc/X11/xdm/Xservers. If you're using gdm (as all sane people
do), you don't have to worry, X is not reniced by gdm.
Thanks Austin! This tip has solved a long-running Audacity 'bug' for
me, which I couldn't figure out. I wasn't seeing it on my
gdm/blackbox studio machine, but my kdm/kde/blackbox office machine
was always affected, no matter which IRQ the soundcard was on or how
many different builds of Audacity I tried. Both were running
otherwise similar Mandrake 9.1 installations.
For the record, with n set to -10 I got consistent skip-forwards of
the Audacity cursor during playback, whenever I moved the mouse.
That's why I was thinking it was an IRQ problem, but it persisted
even with optimised IRQs (10 for the soundcard, 11 for the network
card, 12 for the mouse.)
I was able to replicate this on two very different hardware machines
running kdm, so other Mandrake 9.1/Audacity users must have been
affected. I'll post the fix to the Audacity lists.
Cheers!
Daniel
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8 comments
5 participants
participants (5)
-
Austin -
Daniel James -
Florian Schmidt -
Joe Button -
Robert Jonsson