[TUHS] PDP-11 legacy, C, and modern architectures

Theodore Y. Ts'o tytso at mit.edu
Fri Jun 29 08:29:54 AEST 2018

On Thu, Jun 28, 2018 at 05:03:17PM -0400, Perry E. Metzger wrote:
> Tens of thousands of machines is a lot more than one. I think the
> point stands. This is the age of distributed and parallel systems.

This is the age of distributed systems, yes.  I'm not so sure about
"parallel".  And the point remains that for many problems, you need
fewer strong cores, and a crapton of weak cores is not as useful.

Of course we should parllelize work where we can.  The point is that
very often, we can't.  And if you are really worried about potential
problems with Spectre and Meltdown, what that means is that sharing
caches is perilous.  So if you have 128 wimpy cores, you need 128
separate I and D cacaches.  If you have 32 stronger cores, you need 32
separate I and D caches.

And the fact remains that humans really suck at parallel programming.
Use a separate core for each HTTP request, with a load balancer to
split the incoming request to tens of hundreds servers?  Sure!  But
using a several dozen cores for each HTTP request?  That's a much
bigger lift.

You're conflating "distributed" and "parllel" computing, and they are
really quite different.

      	    	     	  	    	   - Ted

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