[linux-elitists] ME roadshow
Thu Aug 31 00:44:36 PDT 2000
Paul J Collins writes:
> Linux already has enough latencies, even in 2.4. More are not needed.
Another major quibble: Linux is not realtime. Realtime nowadays means
response times *well* under 1 us, whereas on 2.0/i486DX2(66)
task max min
sched_getscheduler() 165-150 us
open(file) 300-145 us
close(file) 190-145 us
write(1 Byte) 250-150 us
read(1 Byte) 195-150 us
access() 280-150 us
shmget() 200-150 us
While most of this is architecturally artefacted, at least some of it
is due to bloat. RTLinux is no solution. What one needs is a minimal
(OS-independent) kernel, hand-coded in pure assembly, by the designers
of the CPU, which, presumably, have been designing it with above
nanokernel in mind.
> Ingo Molnar (and possibly others) has been doing work on this, but I
> can't get a kernel built with his patch applied to work. Shame.
> Certainly. No operating system kernel is going to be appropriate for
> all situations. A nice microkernel fits the bill there.
The point is: a QNX system will certainly perform no worse than a
Linux system. And a QNX-type system will do on above million-processor
(btw, IBM's Blue Gene will have over one million processors), whereas
vanilla Linux won't.
> However, I'm talking about super-servers derived from pre-existing
> operating systems, which will be roughly the same size as the
> equivalent kernel. Running Linux or BSD on a microkernel buys you
Monolithic superservers are obsolete at the high end. Even with
Myrinet current clustering sucks, but future CPUs will have message
passing in hardware with many GBps and 10-30 ns instead of current
10-30 us. SMP has pretty much arrived, but in near future you ought to
be able to buy a Beowulf with several 10 CPUs in a single tower,
without having to resort to 19" rackmount monstrosities.
> I shine my torch around, and I see big signs saying ``Paul's Ignorance
> Starts Beyond This Line''. Embedded and distributed system are
> another thing I'm not qualified to have an opinion about.
Look, I'm dumb as dirt, but this doesn't mean I can't
criticize. People *should* be thinking ahead when designing
stuff. Maybe in the year 2000 we ought to be able to obtain a
distributed message-passing real-time system. And if PC hardware
sucks, you can always use DSP clusters.
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