Re: [2.4.17/18pre] VM and swap - it's really unusable

Rob Landley
2002-01-10T18:10:29Z

On Wednesday 09 January 2002 09:25 pm, Alan Cox wrote:
> > Do you want an operating system capable of running real-world code
> > written by people who know more about their specific problem domain
> > (audio) than about optimal coding in general, or do you want an operating
> > system intended to only run well-behaved applications designed and
> > implemented by experts?
>
> I want an OS were a reasonably cluefully written audio program works. That
> to me means aiming at the 1mS latency mark. Which doesn't seem to be
> needing pre-empt. Beyond a typical 1mS latency you have hardware fun to
> worry about, and the BIOS SMM code eating you.

I don't know what BIOS SMM code is, or what you mean by "hardware fun". But
the worst audio dropouts I have are "cp file.wav /dev/audio" when I forgot to
kill cron and updatedb started up. (This is considerably WORSE than mp3
playing.) I take it "cp" is badly written? :)

And a sound card with only 1mS of buffer in it is definitely not useable on
windoze, the minimum buffer in the cheapest $12 PCI sound card I've seen is
about 1/4 second (250ms). (Is this what you mean by "hardware fun"?) Even
if the app was taking half that, it's still a > 100ms big gap where the OS
leaves it hanging before you get a dropout. (Okay, some of that's watermark
policy, not sending more data to the card until half the buffer is
exhausted...) What sound output device DOESN'T have this much cache? (You
mentioned USB speakers in your diary at one point, which seemed to be like
those old "paralell port cable plus a few resistors equals sound output"
hacks...)

Now VIDEO is a slightly more interesting problem. (Or synchronizing audio
and video by sending really tiny chunks of audio.) There's no hardware
buffer there to cover our latency sins. Then again, dropping frames is
considered normal in the video world, isn't it? :)

Rob