Date: Sun, 9 Nov 1997 17:10:05 -0700 (MST) From: Nate Williams <nate@mt.sri.com> To: "John S. Dyson" <toor@dyson.iquest.net> Cc: nate@mt.sri.com (Nate Williams), freebsd-smp@freebsd.org Subject: Re: Best processor? Message-ID: <199711100010.RAA06734@rocky.mt.sri.com> In-Reply-To: <199711092359.SAA27521@dyson.iquest.net> References: <199711092339.QAA06530@rocky.mt.sri.com> <199711092359.SAA27521@dyson.iquest.net>
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> > > Therefore bus utilization is likely less with the PII. Even in the > > > case of a 512K cache, the bus utilization is going to be nearly the > > > same. > > > > Not quite. The PII has to 'spin' alot more waiting for data since it > > can't get to it at bus-speeds, while the PPro doesn't have to. Going > > from 256 -> 512K doesn't equal a double in cache performance (I'd > > suspect somewhere around 15-20% at best), so I would think the two #'s > > would be close to break-even. If you get a 512K PPro it would be a big > > win. > > Bus utilization doesn't have as much to do with the processor as what > the processor appears to be to the memory subsystem. A 512K PPro should > have a bus utilization similar to a 512K PII. Sure, the traffic between > the processor and 2nd level cache will be slower (due to the 1/2 speed) > and different (due to the double sized 1st level cache.) That isn't what > I said though. True. But, the 'speed' of the system is only partially related to the bus utilization. > > > 2) Expect about 3-5% miss rate with an 8K or 16K 1st level cache. (I > > > have really measured it on real applications.) > > > > Heck, let's use the #'s from Hennessy and Patterson... > > Sorry, but I measured it running real programs, like gcc, etc. Note that > I seldom saw an 11% L1 miss rate (of course, you can make it miss using > synthetic benchmarks, but that is not what I am talking about.) My version of the book is pretty old, and much has been done since then, but the principles are still valid. .. > measured though. What was the line size on those caches? Maybe I'll > finally have to buy a copy of H&P to see what they are talking about. Highly recommended. > > I'd like to see real #'s to back that up. > > Well, someone just posted a benchmark that showed that at least on PII was > faster than my PPro (I think that it was the semspeed benchmark.) That was a 266Mhz PII in UP setup, wasn't it? I expect it to beat it, but in DP (or more), no-one has made any benchmarks. > Now, the only thing that I can believe to be fact at this point: > > a 4-WAY P6 beats all PII configs. > a P6 (per MHz) is mostly faster than a PII. > a P6 system is likely faster than a PII system, if you need > more than 512MB. > a P6-233 is seldom slower than a PII-233. > > I don't think that any claims can be made that in general: > > a dual P6-200 Natoma sys is faster than a dual PII-233 LX system. I remember seeing someone claiming that that was indeed the case, and they had #'s to back it up. And not just a bit faster, *Significantly* faster, so much that if I remember right I was thinking that a 2*PPro@200 would *still* be faster than a 2*PII-266, and possibly even at 300, though that would be a harder one to judge. > If we find out that a dual PII/233 or PII/266 is slower than a dual P6-512K, > that would be VERY INTERESTING!!! Anyone willing to take up the challenge? If I remember right, there are numbers in the archives. Does anyone remember them? I don't have time to wade through the archives (playing with mame right now. :) Nate
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