RE: a joint letter on low latency and Linux

[Russell, Richard]

> Well, I personally would rather see that nobody ever needed RTlinux at
> all. I think hard realtime is a waste of time, myself, and 

The need for hard real-time comes when you have real-world requirements that
require absolute timing garantees with 100% reliability. For eg, a
heart-lung machine needs to send out signals at a perfectly regular time. If
cron suddenly decides to run mkwhatis or something, and you get a minor
unevenness in the signal generated, you have a problem. The other 99.9% of
the time, the CPU will be fast enough to compensate, but you need a 100%
garantee in some situations. (how would it be if once in every 1000 days,
someone on a heart-lung machine dies  because the computer used couldn't
give hard timing garantees?). Yes, most problems (say audio streaming) don't
have this true _hard_ real-time requirement, but some do, and it's these
that really matter. Another thing to consider is that some hard real-time
requirements actually require significant processing, and as such, the
margin for error is much lower, and present CPUs are not "overwhelmingly
fast enough"... :)

<snip>

> I definitely agree with low-latency requirements even in a 
> standard Linux.
> I just disagree violently with doing them with horrible 
> cludges instead of
> working on doing it right.

Absolutely, but there is a need for an OS that can give hard real-time
garantees. Maybe it is innapropriate to try to make Linux do this at once --
if there is no way of doing it that is not a kludge, it probably should be
done using a different kernel. There are some requirements (eg hard
real-time vs efficiency in other situations) that may be fundamentally
incompatible, and should probably be solved separately.

rr