Subject: Re: [linux-audio-dev] mutex madness
From: David Olofson (audiality_AT_swipnet.se)
Date: pe loka 01 1999 - 18:17:12 EDT
On Fri, 01 Oct 1999, David Slomin wrote:
> On Thu, 30 Sep 1999, Paul Barton-Davis wrote:
>
> > Also, when I think about keeping a GUI thread at a lower priority than
> > the DSP engine thread, I am thinking about kernel threads with system
> > scope scheduling, not user level threads with process scope
> > scheduling. To manage the relative priority of a GUI and a DSP thread
> > from user space implies switching the GUI and DSP user threads on and
> > off the same kernel thread(s). If you're using an SMP system, this is
> > a bad idea.
>
> More proof why I should leave such low-level realtime stuff to the
> experts. :-) Thanks.
>
> Here's a derivative question... is there such a thing as a realtime OS
> that is usable by application developers who don't want to have to think
> at such a low level? Conversations about the "evils" of using conditional
> code, for example, make me as an application-level developer lose
> interest.
The "conditional code" thing I'm mentioning every now and then is just about
pure performance, and not really RT-related. The reason why it's important in a
plug-in API is that you certainly don't want overhead built into the design of
a system that you can't avoid. (Guess why I dropped WinNT. *heh...*)
Real time programming for the non-control engineer *is* actually a little more
complicated in a "mixed mode", all purpose system like Linux. For me, working
professionally with embeded RT systems, having a full-blown UNIX just around
the corner, on the same machine is heaven, but it also means you have to keep
in mind that synchronizing to non-RT parts of the system - directly or
indirectly - will break you guaranteed deadlines.
Pure RTOS's (like QNX) are probably a little nicer, as they have a cleaner
design, where you don't have to worry about system calls being problematic, or
even not possible to use from RT tasks, but you still have to code by the laws
of nature, of course. :-)
//David
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