[linux-audio-user] I/O scheduler for 2.6 kernel

[Antonio]

Hi Peder, Mark,

On Wed, 2005-09-28 at 17:03 +0200, Peder Hedlund wrote:
> > I believe that you are using anticipatory.
> 
>  Yes, your using the one in brackets

Yes, I've noted it now ;-)

> >I don't know which one is best for low latency.
> 
>  I don't either, but judging from this it might be anticipatory:
>  http://kerneltrap.org/node/616.
>  I really doubt (from an ordinary audio users POV) you'll see
>  that much difference in latency tough. I'd rather make sure my hdparm
>  values are correct.

I've jet optimised my hd with hdparm. Thanks to remember this though.

> > You can try each one (I think) by adding a boot time option to grub.conf
> > elevator=deadline
> > or
> > elevator=cfq
> 
>  or you can change the running scheduler w/o rebooting by doing
>    echo deadline > /sys/block/hda/queue/scheduler

Ok I've tried and both methods work. Before I was bad spelling the name
of the scheduler so it weren't changed. (I'm not sure if I right spelled
this sentence, though :-( ).

To follow Mark's advice to experiment myself I done a little, non
scientific, test. I've tried to uninstall and reinstall (with apt)
openoffice (~ 150 MB) while listening a good album (say Holy Diver, Dio)
with beep-media-player. I've found that the anticipatory scheduler
gives lots of gaps (too much) in the music during the process. The
deadline scheduler gives less gaps, but there are at least a long gap (~
0.5 sec) during the uninstal-install process. If, in the meantime, I
also open/close evolution the gaps become more and more long. With the
cfq scheduler instead I don't have a single (audible) gap in the music,
also using evolution or other programs during the uninstall-install
process. The noop scheduler is the worse in my test.

This is only my little test. Probably if your aim is to do multi-track
recording with ardour you can have opposite results (regarding wich
scheduler is the best), or the same, I don't know. I've reported it only
for the record.

>  For latency, I'd run the latest 2.6.13 (it's .2 now).
>  2.6.12 had some bugs in its rlimits code that's fixed in 13.
>  Also make sure you have the patched PAM and an adusted
>  /etc/security/limits.conf to make proper use of rlimits.

And yes I'm going to try the 2.6.13 too. Do you know if I can use the
realtime-lsm module with the .13? I don't care about security risk on
this machine.

Anyhow, many thanks for the useful answer you give me so far ;-).

Best Regards,

  ~ Antonio