Low memory bandwidth on Linux-Embedded (ARM)

Question

I am using ARM926EJS. I get 20% faster memory speed in a memory test, without Linux (just like the Getting Started executable). But on Linux, the same code runs 20% slower.

Code

 
/// Below code just performs burst mode memcopy test.        
void asmcpy (void * a, void * b, int iSize)
{
   do
  {
    asm volatile (
             "ldmia% 0 !, {r3-r10} \ n \ t"
             "stmia% 0 !, {r3-r10} \ n \ t"
             : "+ r" (a), "+ r" (b)
             :
             : "r" (r3), "r" (r4), "r" (r5), "r" (r6), "r" (r7), "r" (r8), "r" (r9), "r" (r10)
             );
  } while (size--)
}

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int main()
{
  int a[320 * 120], b[320 * 120];

 for(int i=0; i != 10000; i++)
 {
   /// Size is divided by 8 because our memcpy function performs 8 integer load stores in the iteration
   asmcpy(a, b, (320 * 120) / 8);
 }
}

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Answer 1

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Answer 4

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