Centre Blaise Pascal » HPL sur GPU

/* 

 * -- High Performance Computing Linpack Benchmark (HPL)                

 *    HPL - 2.0 - September 10, 2008                          

 *    Antoine P. Petitet                                                

 *    University of Tennessee, Knoxville                                

 *    Innovative Computing Laboratory                                 

 *    (C) Copyright 2000-2008 All Rights Reserved                       

 *                                                                      

 * -- Copyright notice and Licensing terms:                             

 *                                                                      

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 * modification, are  permitted provided  that the following  conditions

 * are met:                                                             

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 * software must display the following acknowledgement:                 

 * This  product  includes  software  developed  at  the  University  of

 * Tennessee, Knoxville, Innovative Computing Laboratory.             

 *                                                                      

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 * THIS  SOFTWARE  IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,  INCLUDING,  BUT NOT

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 * ---------------------------------------------------------------------

 */ 

/*

 * Include files

 */

#include "hpl.h"

#ifdef STDC_HEADERS

int HPL_numrocI

(

   const int                        N,

   const int                        I,

   const int                        INB,

   const int                        NB,

   const int                        PROC,

   const int                        SRCPROC,

   const int                        NPROCS

)

#else

int HPL_numrocI

( N, I, INB, NB, PROC, SRCPROC, NPROCS )

   const int                        N;

   const int                        I;

   const int                        INB;

   const int                        NB;

   const int                        PROC;

   const int                        SRCPROC;

   const int                        NPROCS;

#endif

{

/* 

 * Purpose

 * =======

 *

 * HPL_numrocI returns  the  local number of matrix rows/columns process

 * PROC  will  get  if  we give out  N rows/columns starting from global

 * index I.

 *

 * Arguments

 * =========

 *

 * N       (input)                       const int

 *         On entry, N  specifies the number of rows/columns being dealt

 *         out. N must be at least zero.

 *

 * I       (input)                       const int

 *         On entry, I  specifies the global index of the matrix  entry

 *         I must be at least zero.

 *

 * INB     (input)                       const int

 *         On entry,  INB  specifies  the size of the first block of th

 *         global matrix. INB must be at least one.

 *

 * NB      (input)                       const int

 *         On entry,  NB specifies the blocking factor used to partition

 *         and distribute the matrix A. NB must be larger than one.

 *

 * PROC    (input)                       const int

 *         On entry, PROC specifies  the coordinate of the process whos

 *         local portion is determined.  PROC must be at least zero  an

 *         strictly less than NPROCS.

 *

 * SRCPROC (input)                       const int

 *         On entry,  SRCPROC  specifies  the coordinate of the  proces

 *         that possesses the first row or column of the matrix. SRCPRO

 *         must be at least zero and strictly less than NPROCS.

 *

 * NPROCS  (input)                       const int

 *         On entry,  NPROCS  specifies the total number of process row

 *         or columns over which the matrix is distributed.  NPROCS mus

 *         be at least one.

 *

 * ---------------------------------------------------------------------

 */ 

/*

 * .. Local Variables ..

 */

   int                        ilocblk, inb, mydist, nblocks, srcproc;

/* ..

 * .. Executable Statements ..

 */

   if( ( SRCPROC == -1 ) || ( NPROCS == 1 ) )

/*

 * The data is not distributed, or there is just one process in this di-

 * mension of the grid.

 */

      return( N );

/*

 * Compute coordinate of process owning I and corresponding INB

 */

   srcproc = SRCPROC;

   if( ( inb = INB - I ) <= 0 )

   {

/*

 * I is not in the first block, find out which process has it and update

 * the size of first block

 */

      srcproc += ( nblocks = (-inb) / NB + 1 ); 

      srcproc -= ( srcproc / NPROCS ) * NPROCS;

      inb     += nblocks * NB;

   }

/*

 * Now  everything  is  just like  N, I=0, INB, NB, srcproc, NPROCS. The

 * discussion goes as follows:  compute my distance from the source pro-

 * cess  so that within this process coordinate system,  the source pro-

 * cess is the process such that mydist = 0, or PROC == srcproc.

 *

 * Find  out  how  many  full  blocks are globally (nblocks) and locally

 * (ilocblk) in those N entries. Then remark that

 *

 * when  mydist < nblocks - ilocblk*NPROCS, I own ilocblk+1 full blocks,

 * when  mydist > nblocks - ilocblk*NPROCS, I own ilocblk   full blocks,

 * when  mydist = nblocks - ilocblk*NPROCS, either the last block is not

 * full and I own it,  or the last block is full and I am the first pro-

 * cess owning only ilocblk full blocks.

 */

   if( PROC == srcproc )

   {

/*

 * I am the source process, i.e. I own I (mydist=0).  When N <= INB, the

 * answer is simply N.

 */

      if( N <= inb ) return( N );

/*

 * Find  out  how  many  full  blocks are globally (nblocks) and locally

 * (ilocblk) in those N entries.

 */

      nblocks = ( N - inb ) / NB + 1;

/*

 * Since  mydist = 0 and nblocks - ilocblk * NPROCS >= 0, there are only

 * two possible cases:

 *

 *   1) When mydist = nblocks - ilocblk * NPROCS = 0, that is NPROCS di-

 *      vides the global number of full blocks,  then the source process

 *      srcproc owns one more block than the other processes;  and N can

 *      be rewritten as N = INB + (nblocks-1) * NB + LNB  with  LNB >= 0

 *      size of the last block. Similarly, the local value Np correspon-

 *      ding to N can be written as  Np = INB + (ilocblk-1) * NB + LNB =

 *      N + ( ilocblk-1 - (nblocks-1) )*NB.  Note  that this case cannot

 *      happen when ilocblk is zero, since nblocks is at least one.

 *

 *   2) mydist = 0 < nblocks - ilocblk * NPROCS, the source process only

 *      owns full blocks,  and  therefore Np = INB + ilocblk * NB.  Note

 *      that when ilocblk is zero, Np is just INB.

 */

      if( nblocks < NPROCS ) return( inb );

      ilocblk = nblocks / NPROCS;

      return( ( nblocks - ilocblk * NPROCS ) ? inb + ilocblk * NB :

              N + ( ilocblk - nblocks ) * NB );

   }

   else

   {

/*

 * I am not the source process. When N <= INB, the answer is simply 0.

 */

      if( N <= inb ) return( 0 );

/*

 * Find  out  how  many  full  blocks are globally (nblocks) and locally

 * (ilocblk) in those N entries

 */

      nblocks = ( N - inb ) / NB + 1;

/*

 * Compute  my distance from the source process so that within this pro-

 * cess coordinate system,  the source  process is the process such that

 * mydist=0.

 */

      if( ( mydist = PROC - srcproc ) < 0 ) mydist += NPROCS;

/*

 * When mydist < nblocks - ilocblk*NPROCS, I own ilocblk + 1 full blocks

 * of size NB since I am not the source process,

 *

 * when mydist > nblocks - ilocblk * NPROCS, I own ilocblk   full blocks

 * of size NB since I am not the source process,

 *

 * when mydist = nblocks - ilocblk*NPROCS,

 * either the last block is not full and I own it, in which case

 *    N = INB + (nblocks - 1)*NB + LNB with  LNB  the  size  of the last

 *    block such that NB > LNB > 0;  the local value Np corresponding to

 *    N is given by  Np = ilocblk*NB+LNB = N-INB+(ilocblk-nblocks+1)*NB;

 * or the  last  block  is  full  and I am the first process owning only

 *    ilocblk full blocks of size NB, that is N = INB+(nblocks-1)*NB and

 *    Np = ilocblk * NB = N - INB + (ilocblk-nblocks+1) * NB.

 */

      if( nblocks < NPROCS )

         return( ( mydist < nblocks ) ? NB : ( ( mydist > nblocks ) ? 0 :

                 N - inb + NB * ( 1 - nblocks ) ) );

      ilocblk = nblocks / NPROCS;

      mydist -= nblocks - ilocblk * NPROCS;

      return( ( mydist < 0 ) ? ( ilocblk + 1 ) * NB :

              ( ( mydist > 0 ) ? ilocblk * NB :

                N - inb + NB * ( ilocblk - nblocks + 1 ) ) );

   }

/*

 * End of HPL_numrocI

 */

}