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On Thu, Sep 01, 2005 at 08:48:41AM +1000, QuantumG wrote:
> I didn't say it was impossible. I said it was insane. Yes, you can
> hack real time scheduling into Linux. Yes, we do have a kernel threads
> and kernel re-entry in Linux. Does Linux have the best architecture for
> such features? Hell no. The result is a massive blob of complexity
> running at the highest privilege level on the system.
>
> As for whether or not a microkernel really made a lot of difference to
> BeOS.. it contributed a lot to the overall system architecture. It let
> the developers compartmentalize concerns into communicating servers more
> readily than a monolithic kernel does.
Don't forget that a microkernel introduces communication overhead and
usually some extra scheduling overhead which in turn eats into performance.
I seem to remember there was a big squabble over who had the fastest
webserver until Linux introduced a kernel level http accelerator which
blew everyone else out of the water so badly that they first tried accusing
the kernel developers of cheating and when that didn't work they just
stopped playing that game, took the ball and went home.
That just happens to be one example of a real time task that Linux turns
out to be rather good at. However, other real time tasks (such as queuing
live music streams) have proven a bit more of a challenge and to some
extent the idea that "real time" means anything specific is in itself
quite wrong because there are a great many different tasks that have
special sorts of time constraints (e.g. low average latency, bounded
worst case latency, consistent latency (low jitter), fast resume
from a power-save state (power efficient), accurate and reliable internal
timing sources, etc) and depending on the situation, different
constraints will become critical.
- Tel
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