[linux-elitists] ME roadshow

Greg KH greg@wirex.com
Thu Aug 31 09:47:41 PDT 2000


On Thu, Aug 31, 2000 at 12:44:36AM -0700, Eugene Leitl wrote:
> 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)

Linux has not ever professed to be "realtime" (and let's not digress
into what the meaning of 'realtime' is...)

> 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.

What is the problem with RTLinux?  It is a great solution for running a
Linux kernel on a processor for an application that needs better latency
than normal Linux can provide (or better latency than NT, or Win95.)

For the application you are speaking of (huge arrays of CPUs doing
nothing but passing messages around) Linux is not the solution.

But I don't think that a hand-coded in assembly kernel is a solution
either.  The code churned out by todays C compilers is much better than
the "average" assembly programmer can create.  And when you have to
maintain that kernel over time... well I have been there, let's just say
that I would never do that again in my lifetime.

> 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.

Ah, but message passing kernels (or microkernels) have the disadvantage
of the fact that all they end up doing well is passing messages very
quickly, not getting any "real work" done.  But I don't know anything
about how the OSs work on those 100+ CPU clusters done by Intel and IBM.
That is a whole arena that is outside of my current knowledge (hell, I
just _finally_ got access to a 2 proc machine for the first time in my
life on Monday.)

Can anyone point me to some links about the OSs in these superscaler
clusters?

OB Linux elitism:
  Linux has prospered over a whole lot of other microkernel OSs due to
  the advantage of it's monolithic kernel.  There is plenty of
  documentation out there proving that for single processors,
  microkernels is _not_ the way to go.


greg k-h

-- 
greg@(kroah|wirex).com




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