F21_vs_Alpha

[jfox@xxxxxxxxxx (Jeff Fox)]

Dear MISC readers,

Mike wrote:

>Yes, maybe I was a little opptimistic here.  I _was_ focusing on integer
>benchmarks because (1) F21 would be trounced in a floating point 
>comparison, and (2) it seems that many applications could be written
>using integer math, based on many comments here and elsewhere.  Of course,
>most scientists and engineers only know or want to use floats.  I have 

I agree with you about floating point.  I hope that if F21 can demonstrate
that it can act as a digital lab instrument it may be useful to some
scientists and engineers will recognize that it may have some
usfulness for this.  Something in between a conventional microcontoller
and a conventional workstation.  Some of the features of a workstation,
some of the features of a microcontroller.  I have seen some very nice
digital instrument software that runs on PCs with an A/D board and
acts like a storage scope or logical analyzer or spectrum analyzer and
I think that that sort of thing might be quite useful on a single
F21 or network of F21.
  
My image of the F21 is something cheap enough to be used in 
embedded apps, and delivering high end PC power as a single chip.
As a multiprocessor fairly high numbers of nodes can be connected
before the network becomes the bottleneck in many applications 
while still staying at low prices.

>not figured out how the F21 compares to Alpha on integer tasks.  Maybe Alpha
>would kill it.  I am hoping that a ring of F21s has a chance.

F21 is not intended to deliver Alpha performance per node. 486DX/4, Pentium,
P6 maybe, but Alpha is the current top of the line.  The 21164 is
listed as potentially getting two integer and two FP instructions
per clock, and at up 300 mhz.  Yes, 1200 mips is the peak advertizing
mips.  Now in discussions in comp.arch where HP and DEC people were
comparing benchmarks the HP guys liked to mention several published
Alpha benchmarks that are getting 3 or 4 clocks per instruction, not
4 instructions per clock.  So although the Alpha might actually
get 600 integer mips on some benchmark in the real world it could
easily drop to 75 or 100 mips.  (yes the thing is 64 bits wide too!)
Likewise F21's 200+ mips is peak advertizing mips.  In the real world
the performance will be 50 mips.  It doesn't take much data memory
access for F21 or out of cache operation on Alpha to see the
real world numbers drop.

Still I like to use Alpha as a comparison of the real difference
between the extemes.  Alpha is BIG, HOT, and EXPENSIVE.  I have
collected chip data spreadsheets, and the differences between
Alpha and F21 just jump out at you.  Watts vs milliwatts, 10M vs
15k transistors, hundreds of times larger and more expensive die
even when Alpha is made with a smaller process.  Basically it
looks like 1000/1.

This does not reflect the fact that to get maximum performance
out of Alpha you need a lot of other very expensive parts like
very fast memory and GAS cache controllers and three levels of
cache etc.  As if starting off with 1000/1 ratio were not
already enough.

I think the Alpha is a great chip, but I can't afford one.  If
you want to make a comparison I think you should say how does
one Alpha compare to 1000 F21?

If you are paying $250,000 per node you definately want the
biggest fastest killer node you can get.   Alpha is one of those
killer type CPU.  If you are spending big bucks then $3K or $4K
for a CPU is a good fit.  You just wouldn't to put a single
$1 CPU on thousands and thousands of dollars worth of memory.

F21 is not designed to run the same software as Alpha, nor is
it going to produce Alpha level performance per node.  It will be
closer on performance than it is on any of the other numbers
in the spreadsheet.  On many problems I expect a few F21 will
get better performance than a single Alpha.

It would be better anyway to compare a P64 type processor to
Alpha.  In .5 or .35 micron a MISC processor could get a clock
with very high speed, and on stack operations run the CPU at
about 13 times the memory speed.  I expect that Chuck will offer
a combination of on-chip ram and rom and multiple busses and
more memory management and multitasking support in the hardware
by the time he is working with 64 bit chips.  But of course it
is hard to predict what will be a priority in the future.
The P64 I describe above would be several times more expensive
than F21, but not several hundred or a thousand times more expensive.

Jeff Fox

peak in
Jeff Fox