Re: Realtime hurd?

[Adam Sampson <azz@gnu.org>]

On Mon, Nov 01, 1999 at 12:47:20PM +0100, Svanberg Liss wrote:
> > >Will it be possible to write hard-realtime applications under hurd[?] I
> > >have heard that it is possible under linux if you link your application
> > >into kernel space like a driver module.
> > This would be very cool. It should support multimedia apps and
> > synchronizing different multimedia streams.
> [...] 
> By the way, I think we are talking about different kind of realtime.
> 
> With "Hard realtime" i mean that the application can preempt the kerenl
> itself. When the application can preempt the OS ( like when you sets
> nicelevel to -20 ) I talk about it as "Soft realtime".

I think what you're referring to as "soft realtime" is just what everybody
else calls "scheduling". :-)

> I don't think you would like to run a multimedia app in hard realtime
> because it would probably violate the stability of the entire system.

I don't agree. What some kernels (QLinux and Nemesis, for instance)
implement, and what the second poster above was referring to, is quality of
service; an application can say to the kernel "I need to produce one block
of audio data every 2ms", and the kernel will guarantee that the application
can do that. As long as you implement limits---you don't want a rogue user
coming along and running a task which requests a 2Gb data transfer from the
hard disk every 1ms---then it shouldn't have any effect on data stability.

This sort of thing in a mainstream OS would make Hurd a great platform for
video and audio editing---and games too. :)

-- 

Adam Sampson
azz@gnu.org