Calling Functions on the CPU to Modify the Coprocessor's Execution Environment

This topic only applies to Intel® Many Integrated Core Architecture (Intel® MIC Architecture).

Some CPU APIs have offload equivalents, each of which take two additional arguments to specify the target type and target number, defined by the following arguments:

target_type

target_type is static. It is recommended to use the following pre-defined default:

DEFAULT_TARGET_TYPE

target_number

The specific coprocessor to target.

An expression whose value is interpreted as follows:

>=0

Executes the statement on a specified target according to the following formula:

target = target-number % number_of_targets

For example, in a system with four targets:

  • Specifying 2 or 6 tells the runtime systems to execute the code on target 2, because the result of 2 % 4 and 6 % 4 is 2.

  • Specifying 1000 tells the runtime systems to execute the code on target 0, because the result of 1000 % 4 is 0.

-1 or no value

Executes the statements on a target selected by the runtime system.

<-1

Reserved.

The offload.h header file defines all the function calls that can be made from the CPU to affect the coprocessor's environment.

This topic uses the CPU API omp_set_num_threads and its offload variations as an example. See also the topics listed below for more CPU APIs.

Example

CPU API
void omp_set_num_threads (int num_threads);
Offload API
void omp_set_num_threads_target (TARGET_TYPE target_type, int target_number, int num_threads);
#include "offload.h"
#include "omp.h"
#include <stdio.h>

int main()
{
        int value, result;

        value = 66;
        omp_set_num_threads_target(TARGET_MIC, 0, value);
        #pragma offload target(mic) out(result)
        #pragma omp parallel
        #pragma omp master
        result = omp_get_num_threads();

        printf("Number of threads on target %d\n", result);
        if (result != value) {
          printf("failed1 result=%d, value=%d\n", result, value);
          return 1;
        }
        return 0;
}
For more complete information about compiler optimizations, see our Optimization Notice.