Intel® Compiler Extension Routines to OpenMP*

Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

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Date 3/22/2024

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Intel® Compiler Extension Routines to OpenMP*

The Intel® compiler implements the following group of routines as extensions to the OpenMP* runtime library:

Get and set the execution environment
Get and set the stack size for parallel threads
Memory allocation
Get and set the thread sleep time for the throughput execution mode
Target memory allocation

The Intel® extension routines described in this section can be used for low-level tuning to verify that the library code and application are functioning as intended. These routines are generally not recognized by other OpenMP-compliant compilers, which may cause the link stage to fail in the other compiler. To execute these OpenMP routines, use the /Qopenmp-stubs (Windows*) or -qopenmp-stubs (Linux*) option.

In most cases, environment variables can be used in place of the extension library routines. For example, the stack size of the parallel threads may be set using the OMP_STACKSIZE environment variable rather than the KMP_SET_STACKSIZE_S() library routine.

NOTE:

A runtime call to an Intel extension routine takes precedence over the corresponding environment variable setting.

Execution Environment

Function	Description
`SUBROUTINE` `KMP_SET_DEFAULTS(STRING)` `CHARACTER() STRING`	Sets OpenMP environment variables defined as a list of variables separated by "\|" in the argument.
`SUBROUTINE KMP_SET_LIBRARY_THROUGHPUT()`	Sets execution mode to throughput, which is the default. Allows the application to determine the runtime environment. Use in multi-user environments.
`SUBROUTINE KMP_SET_LIBRARY_TURNAROUND()`	Sets execution mode to turnaround. Use in dedicated parallel (single user) environments.
`SUBROUTINE KMP_SET_LIBRARY_SERIAL()`	Sets execution mode to serial.
`SUBROUTINE KMP_SET_LIBRARY(LIBNUM)` `INTEGER (KIND=OMP_INTEGER_KIND) LIBNUM`	Sets execution mode indicated by the value passed to the function. Valid values are: 1 - serial mode 2 - turnaround mode 3 - throughput mode Call this routine before the first parallel region is executed.
`FUNCTION KMP_GET_LIBRARY()` `INTEGER (KIND=OMP_INTEGER_KIND) KMP_GET_LIBRARY`	Returns a value corresponding to the current execution mode: 1 - serial 2 - turnaround 3 - throughput

Stack Size

Function	Description
`FUNCTION KMP_GET_STACKSIZE_S()` `INTEGER(KIND=KMP_SIZE_T_KIND) &` `KMP_GET_STACKSIZE_S`	Returns the number of bytes that will be allocated for each parallel thread to use as its private stack. This value can be changed with KMP_SET_STACKSIZE_S() routine, prior to the first parallel region or via the `KMP_STACKSIZE` environment variable.
`FUNCTION KMP_GET_STACKSIZE()` `INTEGER KMP_GET_STACKSIZE`	Provided for backwards compatibility only. Use KMP_GET_STACKSIZE_S() routine for compatibility across different families of Intel processors.
`SUBROUTINE KMP_SET_STACKSIZE_S(size)` `INTEGER (KIND=KMP_SIZE_T_KIND)size`	Sets to `size` the number of bytes that will be allocated for each parallel thread to use as its private stack. This value can also be set via the `KMP_STACKSIZE` environment variable. In order for KMP_SET_STACKSIZE_S() to have an effect, it must be called before the beginning of the first (dynamically executed) parallel region in the program.
`SUBROUTINE KMP_SET_STACKSIZE_S(size)` `INTEGER size`	Provided for backward compatibility only. Use `KMP_SET_STACKSIZE_S(size)` for compatibility across different families of Intel® processors.

Memory Allocation

The Intel® compiler implements a group of memory allocation routines as an extension to the OpenMP runtime library to enable threads to allocate memory from a heap local to each thread. These routines are: KMP_MALLOC(), KMP_CALLOC(), and KMP_REALLOC().

The memory allocated by these routines must also be freed by the KMP_FREE() routine. While you can allocate memory in one thread and then free that memory in a different thread, this mode of operation incurs a slight performance penalty.

Working with the local heap might lead to improved application performance because synchronization is not required.

Function	Description
`FUNCTION KMP_MALLOC(size)` `INTEGER(KIND=KMP_POINTER_KIND)KMP_MALLOC` `INTEGER(KIND=KMP_SIZE_T_KIND)size`	Allocate memory block of `size` bytes from thread-local heap.
`FUNCTION KMP_CALLOC(nelem,elsize)` `INTEGER(KIND=KMP_POINTER_KIND)KMP_CALLOC` `INTEGER(KIND=KMP_SIZE_T_KIND)nelem` `INTEGER(KIND=KMP_SIZE_T_KIND)elsize`	Allocate array of `nelem` elements of size `elsize` from thread-local heap.
`FUNCTION KMP_REALLOC(ptr, size)` `INTEGER(KIND=KMP_POINTER_KIND)KMP_REALLOC` `INTEGER(KIND=KMP_POINTER_KIND) ptr` `INTEGER(KIND=KMP_SIZE_T_KIND)size`	Reallocate memory block at address `ptr` and `size` bytes from thread-local heap.
`SUBROUTINE KMP_FREE(ptr)` `INTEGER (KIND=KMP_POINTER_KIND)ptr`	Free memory block at address `ptr` from thread-local heap. Memory must have been previously allocated with KMP_MALLOC(), KMP_CALLOC(), or KMP_REALLOC().

Thread Sleep Time

In the throughput OpenMP* Support Libraries, threads wait for new parallel work at the ends of parallel regions, and then sleep, after a specified period of time. This time interval can be set by the KMP_BLOCKTIME environment variable or by the KMP_SET_BLOCKTIME() function.

Function	Description
`FUNCTION KMP_GET_BLOCKTIME(` `INTEGER KMP_GET_BLOCKTIME`	Returns the number of milliseconds that a thread should wait, after completing the execution of a parallel region, before sleeping, as set either by the `KMP_BLOCKTIME` environment variable or by KMP_SET_BLOCKTIME().
`FUNCTION KMP_SET_BLOCKTIME(msec)` `INTEGER msec`	Sets the number of milliseconds that a thread should wait, after completing the execution of a parallel region, before sleeping. This routine affects the block time setting for the calling thread and any OpenMP team threads formed by the calling thread. The routine does not affect the block time for any other threads.

Target Memory Allocation

This feature is only available for ifx.

Function	Description
TYPE(c_ptr) FUNCTION omp_target_alloc_host (size, device_num) USE, INTRINSIC :: ISO_C_BINDING INTEGER(c_size_t) :: size INTEGER(c_int) :: device_num	Returns the address of a storage location that is `size` bytes in length allocated in host memory. The same pointer may be used to access the memory on the host and all supported devices. If the allocation request fails, a null pointer is returned.
TYPE(c_ptr) FUNCTION omp_target_alloc_device (size, device_num) USE, INTRINSIC :: ISO_C_BINDING INTEGER(c_size_t) :: size INTEGER(c_int) :: device_num	Returns the address of a storage allocation that is `size` bytes in length. Device allocations are owned by the device specified by `device_numin` device memory if present. Generally, the allocation can be accessed only by the device, but may be copied to other device or host allocated memory. A null pointer return value indicates the allocation was not successful.
TYPE(c_ptr) FUNCTION omp_target_alloc_shared (size, device_num) USE, INTRINSIC :: ISO_C_BINDING INTEGER(c_size_t) :: size INTEGER(c_int) :: device_num	Returns the address of a storage allocation that is `size` bytes in length. The same pointer may be used to access the memory on the host and the specified device. Shared allocations are shared by the host and the specified device, and are intended to migrate between the host and the device. A null pointer is returned if the allocation is unsuccessful.

Function

Description

TYPE(c_ptr) FUNCTION omp_target_alloc_host (size, device_num)

USE, INTRINSIC :: ISO_C_BINDING

INTEGER(c_size_t) :: size

INTEGER(c_int) :: device_num

Returns the address of a storage location that is size bytes in length allocated in host memory. The same pointer may be used to access the memory on the host and all supported devices. If the allocation request fails, a null pointer is returned.

TYPE(c_ptr) FUNCTION omp_target_alloc_device (size, device_num)

USE, INTRINSIC :: ISO_C_BINDING

INTEGER(c_size_t) :: size

INTEGER(c_int) :: device_num

Returns the address of a storage allocation that is size bytes in length. Device allocations are owned by the device specified by device_numin device memory if present. Generally, the allocation can be accessed only by the device, but may be copied to other device or host allocated memory. A null pointer return value indicates the allocation was not successful.

TYPE(c_ptr) FUNCTION omp_target_alloc_shared (size, device_num)

USE, INTRINSIC :: ISO_C_BINDING

INTEGER(c_size_t) :: size

INTEGER(c_int) :: device_num

Returns the address of a storage allocation that is size bytes in length. The same pointer may be used to access the memory on the host and the specified device. Shared allocations are shared by the host and the specified device, and are intended to migrate between the host and the device. A null pointer is returned if the allocation is unsuccessful.

Parent topic: OpenMP* Library Support

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