Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!olivea!apple!agate!sprite.berkeley.edu!elm From: elm@sprite.berkeley.edu (ethan miller) Newsgroups: comp.benchmarks Subject: Re: bc is bs Message-ID: <1990Dec7.085938.15942@agate.berkeley.edu> Date: 7 Dec 90 08:59:38 GMT References: <1990Dec6.133344.2544@cs.utk.edu> <109969@convex.convex.com> Sender: usenet@agate.berkeley.edu (USENET Administrator) Reply-To: elm@sprite.berkeley.edu (ethan miller) Organization: Berkeley--Shaken, not Stirred Lines: 32 In article <109969@convex.convex.com> tighe@convex.com (Mike Tighe) writes: %Not only is the benchmark itself worthless, but so are the times reported %by the benchmarkers. Why? Because the benchmark requires elapsed (real) %times to be reported, and this number can only be reliable when the %benchmark is run in dedicated mode. Look at these two examples: % %Cray Y-MP (6ns) 5.0 elm@sprite.Berkeley.EDU %Cray YMP4/64 5.9 xxdon@monet.lerc.nasa.gov In the case of the Y-MP that I reported, I used the user+system time charged to the program. The Y-MP has a cycle counter (and the /bin/time command reports charged cycle counts), so I *know* the number I reported is accurate. I didn't report elapsed wall clock time, as it would depend a lot on how loaded the machine was. %An advantage the RISC machines have is that they most likely to be personal %workstations, therefore when bc is run they are already in a "dedicated %mode". Another advantage workstations have is that they are as fast on scalar code. I'm sure bc was taken straight from Unix and unoptimized--after all, how many Cray cycles are spent running bc? The startup latency for memory requests on supercomputers is relatively high. If the program uses non-vector accesses, each memory reference can cost nearly 20 cycles (~120ns for a Y-MP). This is more than the access time from cache of a load-store RISC architecture. ethan ================================= ethan miller--cs grad student elm@sprite.berkeley.edu #include {...}!ucbvax!sprite!elm Witty signature line condemned due to major quake damage.