IBM ESSLPESSL

1
IBM ESSL/PESSL

• Bob Sinkovits
• Scientific Computing Department
• SDSC
• All hands Meeting
• February 24-28, 2001

2
Engineering and Scientific Subroutine Library
(ESSL)

• Collection of mathematical subroutines that
  provides over 400 high-performance mathematical
  functions

• BLAS
• Matrix operations
• Linear solvers (Axb)
• Eigensystems
• FFTs, convolutions, etc.

• Sorting and searching
• Numerical quadrature
• Random number generation
• Interpolation

3
Why use ESSL?

• ESSL routines have been specifically tuned for
  IBM architecture and should be your first
  choice. Much faster than downloading and
  compiling LINPACK!One exception comes to mind
  I would personally use SPRNG (Scalable parallel
  random number generator) for random number
  generation http//sprng.cs.fsu.edu/

4
Using ESSL

• Insert ESSL calls into your C or Fortran program
• Link C or Fortran codes with -lessl
• Special C considerations
• Need the line include ltessl.hgt
• Scalars args that are not modified passed by
  value
• Arrays, modified scalars, function names passed
  by reference
• ESSL routines expect multidimensional arrays to
  be stored in column-major (Fortran style) order

5
Using ESSL in threaded codes

• Need to link with -lessl_r to get threadsafe
  libraries
• Using threaded ESSL when binding threads to
  processors can yield some unexpected behavior.
  Master thread may try to spawn its own threads,
  all of which run on a single processor parallel
  region call essl_routine(a,b,c) !Bad performance
  parallel region

6
PESSL

• PESSL parallel ESSL, IBMs numerical library
  for distributed memory parallel applications.
  Contains subset of ScaLAPACK

• PBLAS (levels 2 and 3)
• Linear solvers (Axb)
• Eigensystems
• FFTs
• Random number generation
• BLACS

7
Using PESSL

• Insert PESSL calls into your C or Fortran program
• Link C or Fortran codes with -lpessl
• Special C considerations
• Need the line include ltpessl.hgt
• Scalars args that are not modified passed by
  value
• Arrays, modified scalars, function names passed
  by reference
• ESSL routines expect multidimensional arrays to
  be stored in column-major (Fortran style) order

8
Useful ESSL/PESSL links

• ESSL documentationhttp//www.austin.ibm.com/resou
  rce/aix_resource/sp_books/essl/sessl/essl312/essl
  002.html
• PESSL documentationhttp//www.austin.ibm.com/reso
  urce/aix_resource/sp_books/essl/pessl/pessl212/pe
  ssl002.html