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

[Perry E. Metzger]

So lets not forget: the original question was, do people need to do a
lot of parallel and concurrent computing these days. Keep that in
mind while thinking about this.

On Thu, 28 Jun 2018 09:02:02 -0700 Larry McVoy <lm at mcvoy.com> wrote:
> But for people who care about performance, and there are a lot of
> them, more but slower is less desirable than less but faster.

Sure, but where can you get fewer but faster any more? Yes, you can
get it up to a point, but that point tops out fast. Yes, you can get a
4GHz processor from Intel instead of a bunch of fairly low end
Broadcom ARM chips. However, that top end Intel chip isn't much faster
than it was a few years ago, and it's a pretty cheap and slow chip
compared to what people need, so one of them still isn't going to do
it for you, and so you still need to go parallel, and that means you
still need to write parallel code.

Thirty years ago, you could pay as much money as you wanted, up to
tens of millions, to get a faster single CPU for your work. The
difference between the processors on an IBM PC class machine and on a
Cray was Really Really Different. These days, Intel won't sell you
anything that costs more than a couple thousand dollars, and that
couple thousand dollar thing has many CPUs. The most you can pay per
core, for the highest end, is in the low hundreds depending on the
moment. Taking inflation into account, that's a silly low amount of
money. IBM will sell you some slightly more expensive high end POWER
stuff, but very few people buy that and besides that, there's pretty
much nothing.

So it doesn't matter even if you'd rather spend 100x to get a core
that's 10x faster than the top of what is offered, the 10x faster
thing doesn't exist. You're stuck. You've got top of the line 64 bit
x86 and maybe POWER and there's nothing else. 

So, yes, I agree, all things being equal, people will prefer to buy
the faster stuff, but at the moment, no one can get it, so instead,
we're in an age of loads of parallel machines and cores. Your maximal
fast core is in the hundreds of dollars, but you've got millions of
dollars of computing to do, so you buy tons of processors instead.

> People still care about performance and always will.  Yeah, for your
> laptop or whatever you could probably use what you have for the next
> 10 years and be fine.   But when you are doing real work, sorting
> the genome, machine learning, whatever, performance is a thing and
> lots of wimpy cpus are not.

For all those pieces of work, people use hundreds, thousands, or
hundreds of thousands of cores, depending on the job. Machine
learning, shotgun sequencing, etc., all depend on parallelism these
days. Sometimes people need to buy top end processors for that, but
even then, they have to buy a _ton_ of top end processors because any
given one is too small to do a significant fraction of the work.

So, circling back to the original discussion, languages that don't
let you express such algorithms well are now a problem.

Perry
-- 
Perry E. Metzger		perry at piermont.com