Subject: Re: [linux-audio-dev] introduction & ideas
From: David Olofson (david_AT_gardena.net)
Date: Sun Mar 10 2002 - 02:31:29 EET
On Saturday 09 March 2002 18.30, Martijn Sipkema wrote:
[...]
> preemtible kernel patch is already in 2.5...
Yes, but that doesn't mean that a timer implementation that will burn
CPU cycles on the remainders of the ISA bus on UP systems is going in
as well...
> > After all, if games, audio applications and other multimedia
> > applications are going to fight for the RTC, and then hog the
> > scheduler with 1024+ Hz "wakeup rates", we have a problem.
> >
> > At that point, it would be a lot more efficient if those
> > applications could just use high resolution software timers
> > (driven by the programmable system timer, something like in KURT,
> > AFAIK), programmed to wake threads up *only when required*, as
> > opposed to "at an arbitrary rate, just high enough to do the
> > job".
>
> I think IBM had a patch that did this because the overhead of
> getting interrupted by the system timer every 10ms was too large
> running a lot of linux kernel images on their servers.
Yeah, I think I've heard that mentioned somewhere... Any idea how
they figured out when would be a good time to consider rescheduling?
> > Is this relevant to other applications than "professional MIDI
> > applications"?
>
> I think so.
Well, in fact, it doesn't look better than that a serious video
driver will need it as well, to simulate the missing retrace sync
IRQ. (In that sense, my partly successful attempts to do it without
accurate scheduling seem a bit "counterproductive", as they might
invalidate one of the few reasons to get highres timers in the
kernel... *heh*)
> > > I really don't think that's necessary. A <<ms accurate time
> > > should be sufficient.
> >
> > Well, it all depends on your definition of "correct MIDI
> > timing"...
>
> <<ms
Well, it doesn't get much better than that, so it seems like we're
basically aiming for the same kind of figures.
The main difference is probably that I'm a hard real time guy, who
prefers when everything is totally deterministic, and things happen
exactly as you schedule them, with any significant jitter being
eliminated by properly designed I/O hardware.
As a result, most current MIDI hardware seems broken to me. :-)
//David
.- M A I A -------------------------------------------------.
| Multimedia Application Integration Architecture |
| A Free/Open Source Plugin API for Professional Multimedia |
`----------------------> http://www.linuxaudiodev.com/maia -'
.- David Olofson -------------------------------------------.
| Audio Hacker - Open Source Advocate - Singer - Songwriter |
`-------------------------------------> http://olofson.net -'
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