[RC5] AXP client slow on RC5

John Campbell jcampbel at lynn.ci-n.com
Thu May 31 20:26:09 EDT 2001


On Thu, 31 May 2001, Gregor Terrie wrote:
> 
> My question is rather simple: Is it normal for a DPW500au (Digital Alpha 
> Workstation at 500Mhz) to  Benchmark for RC5 core #0 (axp bmeyer) 
> 0.00:00:16.60 [806,546.70 keys/sec] ?
> 
> I supposed a 64 bit CPU would be better suited to crunch 64bit RC5 
> blocks... Is the clients code optimised for Linux-Alpha or just ported to 
> Linux-Alpha? What other reasons might cause this 'lack of performance'?
> 
	Some of the RISC chips perform relatively poorly on RC5 due to a
lack of a fast rotate instruction, which RC5 depends heavily on. I'm not
sure if this is the case with the Alpha in particular, but I know Sparc
suffers from this... Sparcs eat DES for lunch, but get humiliated by x86
machines at RC5.

> Might this be OS-dependant? (I could get my alpha to run WinNT, but it 
> wouldn't be fun that way ;-þ)

	Probably not. There's some small overhead in task-switching
efficiency and memory management effectiveness and so on, but it'd only be a
few percent either way. RC5 is, for the most part, a straightforward CPU
workout. 

---
John Campbell
jcampbel at lynn.ci-n.com

QotD:  It's bad luck to be superstitious.


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