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Optimizing Cache Usage 6
6-49
In Example 6-11, eight _mm_load_ps and _mm_stream_ps intrinsics are
used so that all of the data prefetched (a 128-byte cache line) is written
back. The prefetch and streaming-stores are executed in separate loops
to minimize the number of transitions between reading and writing data.
This significantly improves the bandwidth of the memory accesses.
// copy 128 byte per loop
for (j=kk; j<kk+NUMPERPAGE; j+=16) {
_mm_stream_ps((float*)&b[j],
_mm_load_ps((float*)&a[j]));
_mm_stream_ps((float*)&b[j+2],
_mm_load_ps((float*)&a[j+2]));
_mm_stream_ps((float*)&b[j+4],
_mm_load_ps((float*)&a[j+4]));
_mm_stream_ps((float*)&b[j+6],
_mm_load_ps((float*)&a[j+6]));
_mm_stream_ps((float*)&b[j+8],
_mm_load_ps((float*)&a[j+8]));
_mm_stream_ps((float*)&b[j+10],
_mm_load_ps((float*)&a[j+10]));
_mm_stream_ps((float*)&b[j+12],
_mm_load_ps((float*)&a[j+12]));
_mm_stream_ps((float*)&b[j+14],
_mm_load_ps((float*)&a[j+14]));
} // finished copying one block
} // finished copying N elements
_mm_sfence();
Example 6-11 A Memory Copy Routine Using Software Prefetch