linux-mips
[Top] [All Lists]

Re: Linux: the next step

To: lm@gate1-neteng.engr.sgi.com (Larry McVoy)
Subject: Re: Linux: the next step
From: nigel@aa5b.engr.sgi.com (Nigel Gamble)
Date: Mon, 12 Aug 1996 15:59:04 -0700 (PDT)
Cc: jes@machine.engr.sgi.com, sca@refugee.engr.sgi.com, lm@neteng.engr.sgi.com, nigel@cthulhu.engr.sgi.com, alambie@wellington.sgi.com, ariel@cthulhu.engr.sgi.com, linux@yon.engr.sgi.com
In-reply-to: <199608122149.OAA15461@neteng.engr.sgi.com> from "Larry McVoy" at Aug 12, 96 02:49:45 pm
Sender: owner-linux@cthulhu.engr.sgi.com
> : Now wait a minute here.  Read the paper before commenting.
> : They create a "real-time" thread under Linux.  That does not
> : mean that it does anything, that the OS has real time support,
> : etc.  There was nothing particularly new about what it did.
> 
> Here's what they did:  they took over control of interrupt disable/enable
> and dispatch.  They run Linux as a thread and allow you to have 0 or more
> real time threads.   If all you are doing is running Linux, it looked
> to me like there was minimal impact to the performance of the system.
> 
> Real time threads run on the bare hardware, they have little
> integration with the OS, other than a pipe like communications device.
> The programming paradigm is you run two processes, one real time that
> gathers events and stuffs them in the "pipe", and one normal that reads
> events out of the pipe and does time _un_critical processing.

That's fine for one class of real-time problems, but it's not going
to help make the RealAudio player (raplayer) useable on Linux.
RealAudio only has to produce AM radio quality audio from a
28.8kbps input stream, yet I only have to move my mouse into
a new window to get audio drop-out.  The RealAudio application,
together with all the support that it is getting from the kernel
in audio drivers, networking code etc., needs to run at a higher
priority than most of the other stuff that might be going on.
This is also a "real time problem", although a different one
from the "get the O/S out of my way" hard real time crowd.

How will Linux solve this type of problem?

> They can guarentee real time response of 10Khz, with less than 15 usec
> variation.  That was with Linux running a 
> 
>       tar f - /usr | (cd /newusr; tar xf -)
> 
> a web browser, X, etc, etc.  Good luck doing that on IRIX up.  Maybe MP.

We can already do this on MP with User Level Interrupts.

As for UP, stay tuned :-)  (Since this mailing list goes outside
of SGI, I'm not going to say any more.)

-- 
Nigel Gamble       "Are we going to push the edge of the envelope, Brain?"
Silicon Graphics   "No, Pinky, but we may get to the sticky part."
nigel@sgi.com
(415) 933-3109

<Prev in Thread] Current Thread [Next in Thread>