TeaLeaf

• Device selection is done by choosing the devices starting at the index given by cuda_device in tea.in. For example, if there are 2 devices on a system and cuda_device is 0, rank 0 will take device 0 and rank 1 will take device 1.

Extra tea.in flags

Turn on cuda kernel use by putting use_cuda_kernels in tea.in.

Solver flags

• tl_max_iters specifies the number of iterations to do before stopping
• tl_eps specifies the acceptable error level to stop at

Enabling these flags will turn on the relevant solver:

• tl_use_jacobi - use a simple jacobi iteration
• tl_use_cg - use the conjugate gradient method
• tl_use_ppcg - use the polynomially preconditioned conjugate gradient method
• tl_use_chebyshev - use chebyshev solver after running a few iterations of the conjugate gradient solver (not preconditioned) to approximate eigenvalues. The number of iterations of CG to run before switching to the chebyshev solver can be specified with the tl_chebyshev_steps flag (eg, tl_chebyshev_steps=20)
• tl_use_preconditioner_type - specify a preconditioner. Current options 'none', 'jac-diag' (Diagonal Jacobi) or 'jac-block' (Block Jacobi)

TODO

• Make preconditioner selectable from tea.in and not a compile time flag

Compiling

• In many case just typing make in the required software version will work.

If the MPI compilers have different names then the build process needs to notified of this by defining two environment variables, MPI_COMPILER and C_MPI_COMPILER.

For example on some Intel systems:

make MPI_COMPILER=mpiifort C_MPI_COMPILER=mpiicc

Or on Cray systems:

make MPI_COMPILER=ftn C_MPI_COMPILER=cc

OpenMP Build

All compilers use different arguments to invoke OpenMP compilation. A simple call to make will invoke the compiler with -O3. This does not usually include OpenMP by default. To build for OpenMP for a specific compiler a further variable must be defined, COMPILER that will then select the correct option for OpenMP compilation.

For example with the Intel compiler:

make COMPILER=INTEL

Which then append the -openmp to the build flags.

Other supported compiler that will be recognise are:-

• CRAY
• SUN
• GNU
• IBM
• PATHSCALE
• PGI

The default flags for each of these is show below:-

• INTEL: -O3 -ipo
• SUN: -fast
• GNU: -ipo
• XL: -O5
• PATHSCLE: -O3
• PGI: -O3 -Minline
• CRAY: -em Note: that by default the Cray compiler with pick the optimum options for performance.

Other Flags

The default compilation with the COMPILER flag set chooses the optimal performing set of flags for the specified compiler, but with no hardware specific options or IEEE compatability.

To produce a version that has IEEE compatiblity a further flag has to be set on the compiler line.

make COMPILER=INTEL IEEE=1

This flag has no effect if the compiler flag is not set because IEEE options are always compiler specific.

For each compiler the flags associated with IEEE are shown below:-

• INTEL: -fp-model strict –fp-model source –prec-div –prec-sqrt
• CRAY: -hpflex_mp=intolerant
• SUN: -fsimple=0 –fns=no
• GNU: -ffloat-store
• PGI: -Kieee
• PATHSCALE: -mieee-fp
• XL: -qstrict –qfloat=nomaf

Note that the MPI communications have been written to ensure bitwise identical answers independent of core count. However under some compilers this is not true unless the IEEE flags is set to be true. This is certainly true of the Intel and Cray compiler. Even with the IEEE options set, this is not guarantee that different compilers or platforms will produce the same answers. Indeed a Fortran run can give different answers from a C run with the same compiler, same options and same hardware.

Extra options can be added without modifying the makefile by adding two further flags, OPTIONS and C_OPTIONS, one for the Fortran and one for the C options.

make COMPILER=INTEL OPTIONS=-xavx C_OPTIONS=-xavx

Finally, a DEBUG flag can be set to use debug options for a specific compiler.

make COMPILER=PGI DEBUG=1

These flags are also compiler specific, and so will depend on the COMPILER environment variable.

So on a system without the standard MPI wrappers, for a build that requires OpenMP, IEEE and AVX this would look like so:-

make COMPILER=INTEL MPI_COMPILER=mpiifort C_MPI_COMPILER=mpiicc IEEE=1 \
OPTIONS="-xavx" C_OPTIONS="-xavx"