This project was written to support my quest to achieve the theoretical best memory bandwidth for reads and writes on my machine, as described in my blog post. For a Retina Macbook Pro, I expect 25.6 GB/s (23.8 GiB/s).

I've tried a number of approaches:

• read_memory_loop does a simple for (i = 0; i < size; *i++);
• read_memory_sse uses SSE packed aligned loads to read 16 bytes at a time.
• read_memory_avx use AVX packed aligned stores to read 32 bytes at a time.
• write_memory_loop does a simple for (i = 0; i < size; *i++ = 1);
• write_memory_rep_stosq forces the use of the rep stosq instruction.
• write_memory_sse uses SSE packed aligned stores to write 16 bytes at a time.
• write_memory_nontemporal_sse uses nontemporal SSE packed aligned stores to write 16 bytes at a time and bypass the cache.
• write_memory_avx uses AVX packed aligned stores to write 32 bytes at a time.
• write_memory_nontemporal_avx uses nontemporal AVX packed aligned stores to write 32 bytes at a time and bypass the cache.
• write_memory_memset is merely a wrapper for memset.

In addition, I tried wrapping all the above in OpenMP to use multiple cores. The function *_omp represent the OpenMP wrapped function *. To enable this, compile the flags -DWITH_OPENMP -fopenmp.

Compiling this code requires a reasonably advanced version of gcc or clang (although clang does not support OpenMP).

./memory_profiler
           read_memory_rep_lodsl:  4.80 GiB/s
                read_memory_loop: 10.66 GiB/s
                 read_memory_sse: 13.44 GiB/s
                 read_memory_avx: 13.60 GiB/s
        read_memory_prefetch_avx: 15.06 GiB/s
               write_memory_loop: 12.84 GiB/s
          write_memory_rep_stosl: 19.22 GiB/s
                write_memory_sse:  8.93 GiB/s
    write_memory_nontemporal_sse: 12.83 GiB/s
                write_memory_avx:  8.91 GiB/s
    write_memory_nontemporal_avx: 12.65 GiB/s
             write_memory_memset: 12.84 GiB/s
       read_memory_rep_lodsl_omp: 19.01 GiB/s
            read_memory_loop_omp: 22.03 GiB/s
             read_memory_sse_omp: 22.18 GiB/s
             read_memory_avx_omp: 22.21 GiB/s
    read_memory_prefetch_avx_omp: 22.19 GiB/s
           write_memory_loop_omp: 22.13 GiB/s
      write_memory_rep_stosl_omp: 21.25 GiB/s
            write_memory_sse_omp:  9.70 GiB/s
write_memory_nontemporal_sse_omp: 22.13 GiB/s
            write_memory_avx_omp:  9.70 GiB/s
write_memory_nontemporal_avx_omp: 22.13 GiB/s
         write_memory_memset_omp: 22.14 GiB/s