Re: Remote fork() and Parallel programming

Larry McVoy (lm@bitmover.com)
Mon, 15 Jun 1998 08:39:26 -0700

: > Process migration on SMP is a horrible idea. As I have mentioned
: > repeatedly, read any one of the dozens of papers on a cache affinity.
: > They all show how in almost all cases, the absolute worst thing you
: > could do for performance is to reschedule a process on another CPU.
:
: Its a matter of time scales. Leaving a cpu idle for 60 seconds with two
: jobs on another CPU is bad on a conventional SMP box - by then cache
: affinity is noise in the efficiency graph.

Quick - name me one parallel computation that would leave a CPU idle
for 60 seconds while the other ones are busy on an SMP. The point?
All the parallel computations I've seen statically load balance at
initialization time and then never move.

I agree that there are other types of parallel loads, but they
tend to be more of the time sharing sort. I don't think anyone
is suggesting that migrating vi or sendmail is a good idea. Right?

: The same is going to be true for dynamic load balancing - if you are talking
: about this sort of balancing on large enough timescales it will make sense
: - true it may be every 30 minutes and you may try to do minimal movement

So explain to me what application will be nicely balanced for 30
minutes and then need to be moved to be balanced? How would one go
about deisgning such an application?

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