Author: Bernhard Bauer
Date: 23:37:13 09/03/00
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On September 03, 2000 at 23:02:51, Robert Hyatt wrote: >On September 03, 2000 at 20:13:57, Aaron Gordon wrote: > >>What about with channel bonding in linux? For example you could get 6 100mbit >>nic's per pc to have 0.6Gbit (or if you've got some serious cash then 6 1gbit >>NICs). As soon as I get some money I'm going to try to experiment with the small >>linux cluster I've got here, maybe go with three 100mbit nics per pc. >>Anyway, it's a thought.. should help the bandwidth problem a lil'.. > > >No, sorry. Totally wrong idea. The PCI bus _is_ the problem. It can >sustain about 100mbytes/second. If you put 6 NICS in the machine, you >are talking about roughly 10mbytes/sec per nic and you really can't drive >the things at 100mbits/sec... I have been able to get roughly 70 mbits/sec >as an upper bound. You could go to something faster (giganet) but then you >run into the PCI bus limit, and trying to bond more than one of those will >result in bus saturation... at the 100mbytes/second limit... > >We are talking about the max bandwidth between the CPU and memory, which is >the bottleneck in the PC, and that is also where the C90 totally cooks the >PC. IE the C90 has 16 cpus at a 2ns clock cycle (500mhz roughly). In one >clock cycle, the machine can do 4 64 bit memory reads, and two 64 bit memory >write. If you multiply that out, that is 48 bytes per cycle, times 16 cpus, >which is 500,000,000 * 48 * 16. Compare that memory bandwidth to the PC >bandwidth and you see why the C90 came out at 30 million dollars when they >were first delivered. That is roughly 4 x 10^11 bytes per second... > >400,000,000,000 bytes per second. Think about that number for a second. 400 >gigabytes per second... compared to 100 megabytes per second... > >:) > >Then you realize just how far the PCs have to go... A look at Jack J. Dongarra's benchmark gives the following line for the C90: Cray C90 (16 proc. 4.2 ns) 479 mflops 10780 mflops in TPP 15238 mflops theoretical peak. So it looks like that old machine was running at 4.2 nanoseconds. My Pc running at 450 Mhz gives 218 mflops when solving a system of linear equations with a size of 1000. However, mflops are pretty useless for chess programming. 16 procs will not make a chessprogram 16 times faster, but maybe 10 times faster. Kind regards Bernhard
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