Re: sound & hdd = the usual lowlatency problems

Benno Senoner (sbenno@gardena.net)
Mon, 9 Aug 1999 20:27:49 +0200


Wakko Warner wrote:
> I'm noticing this one one of my machines. When writing to a hard drive, the
> sound drags. The machine I'm on has piix4 ide and an isa scsi card. I'm
> playing sounds from the drive on the scsi card (aha1510 I think is the scsi
> card). I tried writing to both an ide and scsi drive, both drag the sound.
> Sound card is an SB16 pnp /w ide port (not disablable unfortunately). I had
> a similar problem on an isa ide card playing sounds off of the hard drive
> (like 44k 16bit 2ch sound off the drive, sound card was an ess card). My
> home box that this is happneing on is 2.2.7. The one with the isa ide is no
> longer active, but it was running 2.0.36.

Your problem is very likely not hardware related.
The problem lies in the kernel which,while the disk is under stress, does not
run your sound-app for a time which is bigger than your audio buffer,
and therefore the sound skips.

(There is a little possibilty that the problems are hardware related but
this happens only with broken hardware which monopolizes the
bus for too long time , like some old matrox GFX cards, or some old
IDE controllers, but PII class machines should be safe in this respect)

Ingo Molnar found the weak spots in the kernel , and with his patches, he
demonstrated that Linux is able to provide very low scheduling latencies
( = goodbye audio skips :-) ) on a PII class machine +EIDE disks, even under
the highest load.

We can only hope that these enhancements get into mainstream kernel before 2.4.
Just because this enhancement opens up Linux to a new, big class of
realtime-audio/video apps.

regards,
Benno.

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