Re: [9fans] Re: Threads: Sewing badges of honor onto a Kernel

[ron minnich <rminnich@lanl.gov>]

On Mon, 1 Mar 2004, Lucio De Re wrote:

> Surely message passing differs from pointer passing by the mere addition
> of synchronisation?!  In which case I fail to see how Torvalds could
> consider himself a kernel designer and not recognise the chasm between
> them.

In most people's minds message passing passing usually means 'move the
data from this hole here to that hole there'. Of course in any optimized
situation (shared memory) this can be done with pointer hacks. And even in
the optimized situations, message passing libraries as measured are at
least one or two orders of magnitude slower than simple 'hand the pointer
around', esp. on shared-memory and CC-NUMA systems -- I can give you
references, if you wish, or you can google Jim Taft's work at NASA AMES.  
There's a hardware reason for the performance difference. 

Do people care about that difference? Yes! If you just dropped $10-20M on
a computer, do you want to get $500K worth of performance out of it, or
would you rather get more like $10-20M out of it? Your call. Better yet, 
assume your job rests on the decision, then make the decision :-)

Point to Linus on this one, I think. Sorry.

On another note, the Linux guys are not kernel designers in many senses of
that word. From my point of view Linux is an extremely competent
implementation of some really good and some really bad OS ideas -- ranging
from V6 Unix syscall interface to later ideas such as VFS.  And, like it
or not, it works very very well for many people, including the several
thousand systems we have here that run it for high performance computing.
Credit where credit is due.

And, that said, I'm still gradually moving my existence over to Plan 9. 

ron