Subject: Re: [linux-audio-user] Uhm, low latency?
From: Robert Jonsson (robert.jonsson@dataductus.se)
Date: Tue Feb 04 2003 - 11:59:44 EET
Hi Felipe
felipe wrote:
> Ok, ok =)
>
> Thanks everybody for the answers, now I'm a little less confused maybe. I just
> wanted to make it clear that
>
> 1) *I* did echo "1" >/proc/sys/kernel/lowlatency, thus "virtually" enabling
> lowlatency, infact I can't say wether it is really enbled or not just because
> I've set that to 1 instead of 0.
If you can set it I'm pretty sure it's correctly enabled. But there are
many other factors that interfere with true lowlatency. See below...
>
> 2) Those xruns I get are so many! And I get them even when I'm absolutely
> idle, ie. not recording and the such.
>
> 3) Anybody knows where do I get that capabilities patch? I'd prefer to compile
> the kernel myself...
To get lowlatency it isn't necessary to have the capabilities patch. The
xruns you are seeing won't go away with this change. If you are running
your programs from the root account and starting programs with
SCHED_FIFO enabled (for jack this means: jackd -R <args>)
----
There are alot of thing that could be setup in the wrong way, preventing
really low latency. Some examples: The harddisks might not use DMA,
soundcard might not use a good interupt (shared interupts are bad for
instance), The graphics card might suck all power. Otherwise badly
written drivers...
I would recommend that you run the lowlatency benchmark program from
Benno and check what it is that prevents your system from having low
latency.
ftp://ftp.suse.com/pub/projects/alsa/misc/latencytest-0.42+alsa.tar.bz2
You should also read the relevant documents available at
http://www.djcj.org/LAU/guide/index.php
relevant documents include:
The Low-Latency HOWTO (a must)
Installing from scratch HOWTO (very useful and interesting extension)
/Robert
>
> * * *
>
> Question to Fernando: thanks for the Planet CCRMA project, I've tried out some
> rpm's in my tests partition with mandrake. But what's the difference between
> CCRMA and the soon-to-be-released (maybe) RehMuDi? Aren't them more or less
> the same thing? As far as I know DeMuDi (debian version) and RehMuDi (redhat
> version) have lowlatency kernels together with the same large deal of
> multimedia software.
>
> For you debian fans out there, I simply added this line:
> deb http://http.demudi.org woody demudi
> to my sources.list and now I have demudi packages in my apt database :)
>
> Thanks everybody for existing
>
> references:
> http://www.agnula.org
> http://www.demudi.org
>
>
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