[HARDWARE] Anyone Know Prices?

Jameel Akari jakari at fribble.cie.rpi.edu
Fri Oct 15 10:36:31 EDT 1999


On Fri, 15 Oct 1999, Michael Yakovlev wrote:

> my P2-450 does 1.1 Mkeys/s, P3-500 does 1.35, and Alpha 21164A (don't
> know about frequency) does 450 Kkey/s :(((
> Why "very fast processor" Alpha can get so slow performance ???
> Maybe distributed.net write optimal code special for Intel ???

	I assume that this was your question buried in the rest of it..
THis question was answered last week regarding RISC processors, but what
the heck, I've got time.   The Alpha does not have the rotate-bits-left
instruction that the x86 cpus have. This insruction (ROL) is heavily used
by RC5.  On the Alpha (as well as MIPS and I think Sparc, too) it has to
be emulated with a series of shifts.  The end result is it takes twice as
many machine cycles to process a key.

	Judging by your keyrate, your '164A is probably 450MHz or 500MHz.
Takes about 1200 cycles/key.  Also, the RC5 algorithm has enough loops in
it that I'm guessing it confuses the heck out of the multiple-issue,
branch prediction, and out-of-order operation than Alphas have.  

	The reasoning behind not having built-in ROL is to reduce the
number of instructions and complexity of the CPU core.  ROL isn't used
very often in "real-world" applications, so it was sacrificed to make the
more common cases faster. (Amdahl's Law, IIRC)

------------
Jameel Akari
Insert witty comment here
------------
<http://fribble.cie.rpi.edu/~jakari>
ICQ: 27182003


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