Date: Fri, 03 Sep 1999 18:35:08 +1000 From: Tony Griffiths <tonyg@OntheNet.com.au> To: Doug Rabson <dfr@nlsystems.com> Cc: John Polstra <jdp@polstra.com>, alpha@FreeBSD.ORG Subject: Re: relative alpha speed Message-ID: <37CF883C.B81B8FF5@OntheNet.com.au> References: <Pine.BSF.4.10.9909030903580.2081-100000@salmon.nlsystems.com>
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Doug Rabson wrote: > On Thu, 2 Sep 1999, John Polstra wrote: > > > In article <Pine.BSF.4.10.9909012240130.706-100000@salmon.nlsystems.com>, > > Doug Rabson <dfr@nlsystems.com> wrote: > > > On Wed, 1 Sep 1999 jon@cops.com wrote: > > > > > > > I am a little perplexed about all of this. If the performance and > > > > disk space usage are better on intel what benefit do I have using > > > > an alpha instead of an intel... besides just being cooler than all > > > > of my intel friends? > > > > > > Floating point performance rocks compared to intel. > > > > ... until you make the Alpha conform to the IEEE FP rules and handle > > the whole range of numbers it is supposed to handle (-mieee). Then it > > becomes much slower than ix86 once again. I've been disappointed in > > the performance of the Alphas, given that performance is supposed to > > be their strong point. > > I think the problem may be with our compiler. I don't think the penalty > for using -mieee ought to be so high. I wonder how well the Compaq > compiler deals with this. I've been lead to believe that the main problem with ieee format FP is the method of handling exceptions (NANs, etc). Normally, with 'native' FP, exceptions are handled imprecisely while I belive that with ieee FP the default is precise exceptions. Of course with a pipelined architecture, there is a considerable penalty handling precise exceptions (ie. the pipeline has to be drained after each FP operation that could possibly generate an exception!!!). Check to see if there is a conpiler switch for this... And yes, compiling for Alpha object code is going to be considerably slower than for a CISC environment. Tony To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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