User Manual

Compile the library

Normal compile

• type make to detect the CPU automatically. or
• type make TARGET=xxx to set target CPU, e.g. make TARGET=NEHALEM. The full target list is in file TargetList.txt.

Cross compile

Please set CC and FC with the cross toolchains. Then, set HOSTCC with your host C compiler. At last, set TARGET explicitly.

Examples:

On X86 box, compile this library for loongson3a CPU.

`make BINARY=64 CC=mips64el-unknown-linux-gnu-gcc FC=mips64el-unknown-linux-gnu-gfortran HOSTCC=gcc TARGET=LOONGSON3A`

On X86 box, compile this library for loongson3a CPU with loongcc (based on Open64) compiler.

`make CC=loongcc FC=loongf95 HOSTCC=gcc TARGET=LOONGSON3A CROSS=1 CROSS_SUFFIX=mips64el-st-linux-gnu-   NO_LAPACKE=1 NO_SHARED=1 BINARY=32`

Debug version

`make DEBUG=1`

Install to the directory (optional)

Example:

`make install PREFIX=your_installation_directory`

The default directory is /opt/OpenBLAS

Link OpenBLAS library

Link shared library

gcc -o test test.c -I /your_path/OpenBLAS/include/ -L/your_path/OpenBLAS/lib -lopenblas

If the library is multithreaded, please add -lpthread. If the library contains LAPACK functions, please add -lgfortran or other Fortran libs.

Link static library

gcc -o test test.c /your/path/libopenblas.a

Code examples

Call CBLAS interface

This example shows calling cblas_dgemm in C. https://gist.github.com/xianyi/6930656

#include <cblas.h>
#include <stdio.h>

void main()
{
  int i=0;
  double A[6] = {1.0,2.0,1.0,-3.0,4.0,-1.0};         
  double B[6] = {1.0,2.0,1.0,-3.0,4.0,-1.0};  
  double C[9] = {.5,.5,.5,.5,.5,.5,.5,.5,.5}; 
  cblas_dgemm(CblasColMajor, CblasNoTrans, CblasTrans,3,3,2,1,A, 3, B, 3,2,C,3);

  for(i=0; i<9; i++)
    printf("%lf ", C[i]);
  printf("\n");
}

gcc -o test_cblas_open test_cblas_dgemm.c -I /your_path/OpenBLAS/include/ -L/your_path/OpenBLAS/lib -lopenblas -lpthread -lgfortran

Call BLAS Fortran interface

This example shows calling dgemm Fortran interface in C. https://gist.github.com/xianyi/5780018

#include "stdio.h"
#include "stdlib.h"
#include "sys/time.h"
#include "time.h"

extern void dgemm_(char*, char*, int*, int*,int*, double*, double*, int*, double*, int*, double*, double*, int*);

int main(int argc, char* argv[])
{
  int i;
  printf("test!\n");
  if(argc<4){
    printf("Input Error\n");
    return 1;
  }

  int m = atoi(argv[1]);
  int n = atoi(argv[2]);
  int k = atoi(argv[3]);
  int sizeofa = m * k;
  int sizeofb = k * n;
  int sizeofc = m * n;
  char ta = 'N';
  char tb = 'N';
  double alpha = 1.2;
  double beta = 0.001;

  struct timeval start,finish;
  double duration;

  double* A = (double*)malloc(sizeof(double) * sizeofa);
  double* B = (double*)malloc(sizeof(double) * sizeofb);
  double* C = (double*)malloc(sizeof(double) * sizeofc);

  srand((unsigned)time(NULL));

  for (i=0; i<sizeofa; i++)
    A[i] = i%3+1;//(rand()%100)/10.0;

  for (i=0; i<sizeofb; i++)
    B[i] = i%3+1;//(rand()%100)/10.0;

  for (i=0; i<sizeofc; i++)
    C[i] = i%3+1;//(rand()%100)/10.0;
  //#if 0
  printf("m=%d,n=%d,k=%d,alpha=%lf,beta=%lf,sizeofc=%d\n",m,n,k,alpha,beta,sizeofc);
  gettimeofday(&start, NULL);
  dgemm_(&ta, &tb, &m, &n, &k, &alpha, A, &m, B, &k, &beta, C, &m);
  gettimeofday(&finish, NULL);

  duration = ((double)(finish.tv_sec-start.tv_sec)*1000000 + (double)(finish.tv_usec-start.tv_usec)) / 1000000;
  double gflops = 2.0 * m *n*k;
  gflops = gflops/duration*1.0e-6;

  FILE *fp;
  fp = fopen("timeDGEMM.txt", "a");
  fprintf(fp, "%dx%dx%d\t%lf s\t%lf MFLOPS\n", m, n, k, duration, gflops);
  fclose(fp);

  free(A);
  free(B);
  free(C);
  return 0;
}

gcc -o time_dgemm time_dgemm.c /your/path/libopenblas.a

./time_dgemm <m> <n> <k>

Troubleshooting

• Please read Faq at first.
• Please use gcc version 4.6 and above to compile Sandy Bridge AVX kernels on Linux/MingW/BSD.
• Please use Clang version 3.1 and above to compile the library on Sandy Bridge microarchitecture. The Clang 3.0 will generate the wrong AVX binary code.
• The number of CPUs/Cores should less than or equal to 256. On Linux x86_64(amd64), there is experimental support for up to 1024 CPUs/Cores and 128 numa nodes if you build the library with BIGNUMA=1.
• OpenBLAS does not set processor affinity by default. On Linux, you can enable processor affinity by commenting the line NO_AFFINITY=1 in Makefile.rule. But this may cause the conflict with R parallel.
• On Loongson 3A. make test would be failed because of pthread_create error. The error code is EAGAIN. However, it will be OK when you run the same testcase on shell.

BLAS reference manual

If you want to understand every BLAS function and definition, please read Intel MKL reference manual or netlib.org