OpenMP

PV-WAVE Foundation > Programmer Guide > OpenMP

OpenMP

This section discusses OpenMP, which is a specification for a set of compiler directives, library routines, and environment variables that can be used to specify shared memory parallelism in Fortran and C/C++ programs.

note	OpenMP is currently supported in PV-WAVE on Sun Solaris, Microsoft Windows, and Red Hat Enterprise Linux.

OpenMP is a hardware and software vendor supported specification designed to standardize compiler directives required to implement scalable, parallelized code for shared-memory multi-processor systems. One of the best things about OpenMP is the straightforward manner in which you can apply loop-level parallelization to sections of code in existing programs that would otherwise be unsuitable for multi-threading. This is what has been implemented for most of the array operations which take place in PV-WAVE.

To determine if a particular kernel routine supports OpenMP, look for the following logo:

at the top of the routine description within the PV-WAVE documentation. Table 15-1: OpenMP Enabled Functionality lists the OpenMP enabled functionality of PV-WAVE. Besides the parallelized kernel routines previously listed, many Standard Library and some Math Library routines also run faster in parallel since they are built from composites of these kernel routines.

OpenMP Enabled Functionality
ABS Function	DINDGEN Function	Minimum Operator <
ACOS Function	Division Operator /	MOD
ACOSH Function	DOUBLE Function	Multiplication Operator *
Addition Operator +	EQ	NE
ADJOINT Function	EXP Function	NEIGHBORS Function
AFFINE Function	Exponentiation Operator ^	NINT Function
ALOG Function	FINDGEN Function	NOT
ALOG10 Function	FIX Function	OR
AND	FLOAT Function	PRODUCT Function
Array Concatenation Operators [ ]	FLTARR Function	RBFIMSCL Procedure
ARRAYTRACE Function	GE	REBIN Function
ASIN Function	GREAT_INT Function	REFORM Function
ASINH Function	GT	REPLICATE Function
Assignment Operator =	I32ARR Function	RESAMP
ATAN Function	I32INDGEN Function	REVERSE Function
ATANH Function	IMAGINARY Function	SIN Function
AVG Function	INDEX_CONV Function	SINH Function
BINDGEN Function	INDGEN Function	SLICE Function
BOUNDARY	INT32 Function	SMALL_INT Function
BYTARR Function	INTARR Function	SPMVM Function
BYTE Function	INTERPOL Function	SQRT Function
CINDGEN Function	INTRP Function	STDEV Function
CLUSTBOX	LE	Array Subscripting
COMPLEX Function	LINDGEN Function	Subtraction Operator –
COMPLEXARR Function	LINSPACE Function	TAN Function
CONJ Function	LONARR Function	TANH Function
COS Function	LONG Function	Outer Operations
COSH Function	LT	TOTAL Function
CPROD Function	MAKE_ARRAY Function	TRANSPOSE Function
CUMSUM Function	Matrix Multiplication Operator #	vecOverArr_* Functions
DBLARR Function	MAX Function	WHERE Function
DCINDGEN Function	Maximum Operator >	WhereIn Function
DCOMPLEX Function	MIN Function	XOR
DCOMPLEXARR Function

PV‑WAVE provides the user with controls over the two OpenMP runtime parameters most critical to performance (see SET_OMP). These parameters are the number of threads to be used (Nthreads) and a threshold array size below which parallelization will not be considered (Threshold). Nthreads too high can degrade performance with superfluous thread overhead, and Nthreads too low can degrade performance with underused processors. The Threshold parameter prevents the overhead of a superfluous thread being created for the case Nthreads=1. The optimal values for these parameters vary depending on the hardware, operating system, mathematics, data type, and array size. Establishing these parameters for every array operation in a large PV‑WAVE application can be tedious. Fortunately PV‑WAVE can automatically vary these parameters so that they are optimal for any operation. Both the manual and the automatic methods are discussed in the following sections.