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Geoffrey_Q
Beginner
29 Views

data transfer issue on MIC

Hello!

I'm optimizing an application with Xeon Phi 5110P. And its initialization part looks as below:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
	float *W[7];
	float *B[7];
	//float *dW[7];
	//float *dB[7];
} net;

int main(int argc, char *argv[])
{
	int a[8];
	a[:] = 1024;
	//a[:] = 64;
	int arr1[7], arr2[7];
	arr1[0:7] = a[0:7]*a[1:7];
	arr2[0:7] = a[1:7];

	net n1;

	for(int i=0; i<7; i++)
	{
		n1.W = new float[arr1];
		memset(n1.W, 0, arr1*sizeof(float));
		#pragma offload_transfer target(mic:0) in(n1.W:extent(0:arr1) alloc_if(1) free_if(0)) 
		n1.B = new float[arr2];
		memset(n1.B, 0, arr2*sizeof(float));
		#pragma offload_transfer target(mic:0) in(n1.B:extent(0:arr2) alloc_if(1) free_if(0))
	}
	//calculation on phi

	#pragma offload_transfer target(mic:0) out(n1.W[0:7]:extent(0:arr1[0:7]) alloc_if(0) free_if(1))
	#pragma offload_transfer target(mic:0) out(n1.B[0:7]:extent(0:arr2[0:7]) alloc_if(0) free_if(1))

	return 0;
}

In the initialization step, I tried to allocate memory for the arrays of pointers on the host and transfer data to Phi. If I set the elements of array a with 64, the program runs correctly. But when I tried to set array a as 1024 as above, the program gives "offload error: allocation (base=0x10d6010, size=8388608) overlaps with existing allocation (base=0xcd6000, size=8388608)".

I'm wondering whether this problem comes from memory size limits or other reasons.

I'd appreciate if someone could help to explain this problem. thx

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1 Reply
Kevin_D_Intel
Employee
29 Views

The larger size and offload allocation overlap error probably relate to exhausting available resources on the coprocessor. I can reproduce that scenario but at smaller sizes (even <64) I experience a segmentation fault. You did not mention seeing that though. I have to check with others on this.

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