David Olofson schrieb:
> > Correctly, but we were discusing about visualization using OpenGL :-)
>
> Yes, but even some games and other heavy multimedia applications stream from
> disk and/or various forms of dynamic loading of world data. One reason to do
> that is to reduce loading times, so one can't just dismiss this with "but you
> can use more RAM".
<offtopic>
How about a 1 Gig RAM-Disk? :-)
</offtopic>
> > [ 10 ms pause in rt-app ]
> The problem is probably that you're choking the rest of the system until you
> run into a dead end and *have* to sleep for some reason - and at that time,
> you're out for a good while...
Oh, forgotten to tell: "a 10 ms pause in rt-app which is in SCHED_RR
mode".
means: this task will be allways scheduled next, if it desires
the CPU - in this case: when the 10ms sleep is over.
You may call it cooperative multitasking :-)
> QoS in it's simplest form basically means that you can have a certain amount of
> things done within a certain amount of time.
Isn't that exactly the definition for hard real time? :-)
IMHO QoS is this: The operating system guarantees the application
some kinds of services. This might be a minimum network or harddisk
bandwidth, or simply a minimum amount of task slots within
a certain time - "CPU bandwidth", as linux/rt provides.
Ok, this basicaly sound similar to your definition, but
if the provided service is usefull for the application,
that is something completly different!
Example: within a 40 ms period,
30 ms are fixed to the 3D application. So if
your 3D-Card is basicaly strong enough the generate
25 fps with 75% of the CPU computing power, then your
application will run smooth enough for a Men Machine
Interface. If you need a scene redraw rate bounded to
the refresh rate of the screen (because some machinery
has to bother with it) then this doesn't work, of course ...
At least, you are right: to perform QoS, you need some kind
of real time operating system, but for an MMI, it is IMHO sufficient
to have 10-20 ms latency (depending on the application).
But: For many people on this list, 10 ms might sounds like eternity :-)
So IMHO, the "low latency patch enhanced soft real time
capabilities of a linux operating system"
(sounds like a marketing term) should be sufficient for QoS.
Bernhard
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