Intel(R) - Computational and Systems Biology at MIT

10 Intel® Math Kernel Library User’s Guide"threshold" parameter in HPL.dat to a negative number when testing ENDEARLY. There isno point in doing a residual check if the problem ended early. It also sometimes gives abetter picture to compile with -DASYOUGO2 when using -DENDEARLY.You need to know the specifics of -DENDEARLY:— -DENDEARLY stops the problem after a few iterations of DGEMM on the blocksize(the bigger the blocksize, the further it gets). It prints only 5 or 6 "updates",whereas -DASYOUGO prints about 46 or so outputs before the problem completes.— Performance for -DASYOUGO and -DENDEARLY always starts off at one speed,slowly increases, and then slows down toward the end (because that is what LUdoes). -DENDEARLY is likely to terminate before it starts to slow down.— -DENDEARLY terminates the problem early with an HPL Error exit. It means thatyou need to ignore the missing residual results, which are wrong, as the problemnever completed. However, you can get an idea what the initial performance was,and if it looks good, then run the problem to completion without -DENDEARLY. Toavoid the error check, you can set HPL's threshold parameter in HPL.dat to anegative number.— Though -DENDEARLY terminates early, HPL treats the problem as completed andcomputes Gflop rating as though the problem ran to completion. Ignore thiserroneously high rating.— The bigger the problem, the more accurately the last update that -DENDEARLYreturns will be close to what happens when the problem runs to completion.-DENDEARLY is a poor approximation for small problems. It is for this reason thatyou are suggested to use ENDEARLY in conjunction with ASYOUGO2, becauseASYOUGO2 reports actual DGEMM performance, which can be a closerapproximation to problems just starting.The best known compile options for Itanium® 2 processor are with the Intel®compiler and look like this:-O2 -ipo -ipo_obj -ftz -IPF_fltacc -IPF_fma -unroll -w -tpp2-DASYOUGO2: Gives detailed single-node DGEMM performance information. It captures allDGEMM calls (if you use Fortran BLAS) and records their data. Because of this, the routinehas a marginal intrusive overhead. Unlike -DASYOUGO, which is quite non-intrusive,-DASYOUGO2 is interrupting every DGEMM call to monitor its performance. You shouldbeware of this overhead, although for big problems, it is, for sure, less than 1/10th of apercent.Here is a sample ASYOUGO2 output (the first 3 non-intrusive numbers can be found inASYOUGO and ENDEARLY), so it suffices to describe these numbers here:Col=001280 Fract=0.050 Mflops=42454.99 (DT= 9.5 DF= 34.1DMF=38322.78).The problem size was N=16000 with a blocksize of 128. After 10 blocks, that is, 1280columns, an output was sent to the screen. Here, the fraction of columns completed is1280/16000=0.08. Only about 20 outputs are printed, at various places through the10-10