Date: Sun, 4 Jan 1998 15:39:16 -0500 (EST) From: "John S. Dyson" <dyson@FreeBSD.ORG> To: lukas@design.de (Lukas Wunner) Cc: andreas@klemm.gtn.com, lukas@design.de, lem@cantv.net, freebsd-isp@FreeBSD.ORG Subject: Re: [fbsd-isp] Designing for a very large ISP Message-ID: <199801042039.PAA01086@dyson.iquest.net> In-Reply-To: <19980104174553.57475@reactor> from Lukas Wunner at "Jan 4, 98 05:45:53 pm"
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Lukas Wunner said: > performance, especially the VX chipset). Now consider that we'd put > say, 512MB of RAM in the PPro based system, so that's twice as much as > in our Pentium based news box. If there is more real memory, there is > of course also more data to be transferred between the CPU and the memory > per second, but as the PPro boards' memory bandwidth is actually smaller > than the Pentium boards', the memory interface will become a real > bottleneck. As I said, OrionGX boards seem to be a lot better in that > respect, but they are also hard to get. At least that is my experience. > I have done some analysis on PPro memory usage, and one thing that is fairly impressive is that the processor is very well decoupled from memory by the L1/L2 cache. I think that you'd find that a PPro bus is quite a bit less occupied than a typical P5 MB (due to a dual bus, cache/memory) approach. A normal dual P5 will pretty much fully occupy it's memory bus, while a dual P6 will often not. The decoupling appears to be applicable to the PII also, due to it's dual bus architecture, even though the L2 cache is slower than on a P6. That isn't to disagree with you about the lower Natoma memory bandwidth, however, the PPro doesn't need quite as much of it, while leaving more for peripherals. Note that writes happen a lot less often on a PPro/PII, due to the writeback caching, while the write performance of Natoma is where it is most deficient. -- John | Never try to teach a pig to sing, dyson@freebsd.org | it just makes you look stupid, jdyson@nc.com | and it irritates the pig.
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