Lew wrote:
<div class="moz-text-flowed" style="font-family: -moz-fixed">Scott
David Daniels wrote:
the nub of the problem is not on the benchmarks. There is something
to be said for the good old daays when you looked up the instruction
timings that you used in a little document for your machine, and could
know the cost of any loop. We are faster now, but part of the cost of
that speed is that timing is a black art.
Those good old days never existed. Those manuals never accounted for
things that affected timing even then, like memory latency or refresh
time. SRAM cache made things worse, since the published timings never
mentioned cache-miss delays. Though memory cache might seem a recent
innovation, it's been around a while. It would be challenging to find
any published timing since the commercialization of computers that
would actually tell the cost of any loop.
Things got worse when chips like the '86 family acquired multiple
instructions for doing loops, still worse when pre-fetch pipelines
became deeper and wider, absolutely Dark Art due to multi-level memory
caches becoming universal, and
throw-your-hands-up-and-leave-for-the-corner-bar with multiprocessor
NUMA systems. OSes and high-level languages complicate the matter -
you never know how much time slice you'll get or how your source got
compiled or optimized by run-time.
So the good old days are a matter of degree and self-deception - it
was easier to fool ourselves then that we could at least guess timings
proportionately if not absolutely, but things definitely get more
unpredictable over evolution.
Nonsense. The 6502 with static memory was precisely predictable, and
many programmers (working in machine language, naturally) counted on
it. Similarly the Novix 4000, when programmed in its native Forth.
And previous to that, I worked on several machines (in fact, I wrote the
assembler and debugger for two of them) where the only variable was the
delay every two milliseconds for dynamic memory refresh. Separate
control memory and data memory, and every instruction precisely
clocked. No instruction prefetch, no cache memory. What you see is
what you get.
Would I want to go back there? No. Sub-megaherz clocks with much less
happening on each clock means we were operating at way under .01% of
present day.
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