
The overblown frequency vs. cost efficiency trade-off - luu
http://yosefk.com/blog/the-overblown-frequency-vs-cost-efficiency-trade-off.html
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bsder
The problem with higher frequency is the portion of time you spend doing non-
work things.

The amount of time you spend on things like clock skew and setting up pipeline
flip flops is generally _fixed per cycle_. So, let's say that you need 50ps to
cover clock skew and 100ps to cover flip-flop overhead. At 1GHz, you have
850ps to do work over 1ns (one clock cycle in this instance). At 2Ghz, you
have 500ps-100ps-50ps or 350ps per cycle which means that you have 700ps to do
work in 2 cycles at 2GHz.

At 1GHz, you have 850ps of work over the same time that you only have 700ps of
work at 2GHz. That's quite significant.

There are other advantages at 1GHz as well. You burn far less power trying to
keep your clock aligned since you can have a little more slack and still come
out ahead. You also don't have to flop as many intermediate results. etc.

The problem is that we have only recently started caring about amount of work
per (watt/area/cost/etc) instead of simply amount of work (total).

~~~
_yosefk
What you pointed out is significant and I probably should have mentioned it in
the article together with the other things; my point, however, is that these
problems kick in at a higher frequency than those historically reached by many
accelerators and defended as "optimal" by marketing. In your example, 1 GHz is
used as a "nice low frequency" which is a sensible order of magnitude for a
modern process; people often believe that you have to go as low as 400 or 100
MHz. (Again, the numbers vary with process, this is just to illustrate the
extent of the difference between what I think is the reality vs what I think
are the popular beliefs.)

