Author: Robert Hyatt
Date: 07:48:05 08/04/05
Go up one level in this thread
On August 04, 2005 at 08:16:24, Vincent Diepeveen wrote: >On August 04, 2005 at 02:50:32, Mimic wrote: > >>On August 04, 2005 at 02:37:20, Mark jones wrote: >> >>>Can you imagine how would Junior,shredder,fritz would have played if they where >>>deployed on A super computer like this: >>>http://www.top500.org/sublist/System.php?id=7605 >>> >>>If this were possible not only it would kill all the humans I think it would >>>have crushed Hydra to... >>>What do you thisk about it? And was there an attempt to deploy an pc program >>>on asuper computer? >> >> >>How many Rpeak (GFlops) or Rmax (GFlops) on a normal personal computer ? > >Opteron delivers 2 flops per cycle per core. > >without using calculator: >So a 2.2ghz dual core opteron delivers 2.2 * 2 * 2 = 4 * 2.2 = 8.8 gflop >So a quad opteron delivers 4 * 8.8 = 35.2 gflop > >However the comparision is not fair. IBM is always quoting single precision >calculations whereas majority of researchers uses double precision floating >points. I do not believe that is true. I'm not aware of _any_ floating point hardware today that does 32 bit IEEE math. Every processor I have seen does internal calculations in 64 (actually 80) bits of precision. From the early IBM RS 6000 this has been true. I once spent a couple of days trying to understand why using REAL*4 vs REAL*8 in a FORTRAN program made _zero_ difference in how fast it ran, where on an older IBM /370 it made a significant difference since that box actually had 32 bit and 64 bit hardware. > >If you want to know exact definitions of what is a double precision floating >point, look in the ansi-C definitions. > >In reality the researchers assume 64 bits 'double times a 64 bits double >delivering a 64 bits double. > >In reality single precision is less than 32 bits times 32 bits delivering less >than 32 bits worth of information. Why less than? You lose exponent bits in either length, but the exponent is not "lost information"... > >Major cheating happens in those areas of course, for example the highend >processors like itanium2, intel forgot to put a divide instruction at it. Design decision. Cray computers had no divide either. Never caused them to be less than the fastest floating point processor of their time... > >So they can do divisions in certain test programs faster by using some >approximation algorithm delivering less decimals. > >So all those gflops mentionned are basically multiplication-add combinations. > >The CELL processor is supposed to deliver 256 gflop single precision, this is >however less than 30 gflop double precision. > >In reality software isn't optimal so it will be less than 30 gflop. > >Still it is impressive for a processor that is supposed to get cheap. > >The expensive itanium2 1.5Ghz delivers for example 7 gflop on paper. That's also >paper. SGI when presenting results at the 1 juli 2003 presentation of the 416 >processor itanium2 1.3Ghz cpu, made public there that effecitvely it is >2 times faster in gflops for most applications than the previously 500Mhz MIPS >R14000. > >On paper the MIPS delivers 1 gflop at 500Mhz and on paper the 1.3Ghz itanium2 >delivers 5.2 gflop. > >Practical 2 times faster according to SGI. > >NASA had a similar report initially for their own software when running at a 512 >processor partition. > >So all those gflops you have to take with some reservation. Reality is those >supercomputers usually idle for 70% in the first year, they idle 50% in the >second and 3d year, and when they are outdated in the 4th year they are idle for >30%. That is of course all reserved times added and all 'system processors' not >taken into account. In reality they idle more. > >So many of those supercomputers are paper hero's which the researchers litterary >use to "run their application faster than it would run on a pc". > >There is real few applications that are utmost optimized. Certain matrix >calculation type libraries are pretty good and are pretty optimal for it. > >For those researchers those gflops *really* matter. > >You can count them at 1 hand. Wrong. You need to get out more. Labs like Livermore and Los Alamos have _thousands_ of carefully hand-optimized programs for specific computer architectures. They care whether a program runs in 2 weeks or 6 weeks. Or longer. > >What matters is they have the POSSIBILITY to run their application real real >fast if they want to, and that is real important. > >This big 12288 ibm supercomputer 'blue gene' boxes (6 racks of 2048 processors) >has a cost price of just 6 million euro. > >That's real little if you consider the huge calculation power it delivers for >those researchers it matters for. > >Best usages of those supercomputers are nucleair explosions (i did not say >university groningen is running nucleair simulations) and calculating for >example where electrons in materials are. > >Usually the homepage supports 'biologic' supercomputers. In reality just real >little system time goes to medicines and biologic research, about 0.5% system >time, according to this supercomputer report europe (including all scientific >supercomputers in entire europe). > >Amazingly much system time goes to all kind of weather or extreme climate >simulations. Like they have been calculating world wide so so much already at >what the height of the seawater will become. I became real real sick from that, >as i could not test diep until the world champs itself, because some weather >simulation was nonstop running. > >After they had run at 350+ processors for months (450000 cpu hours or so, >according to official project papers) and after they had created a new discovery >series from the output that sea water would rise 1 meter the coming 100 years, >they discovered a small bug in the initializing data. > >They had initialized the sea water 1 meter too high when starting the test half >a year earlier. > >This was the reason diep ran buggy the first 7 rounds in world champs 2003. > >Vincent
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