[gem5-users] Cache Benchmark in Gem5

[Aaron Vose via gem5-users]

I'm wondering if the following code looks reasonable as a benchmark to test 
performance of L1D cache in Gem5. Changing the size of the L1 cache in Gem5 
(from 32KiB to 1KiB) doesn't seem to show any significant change in the 
benchmark performance (~1%). I would have thought that using a 1KiB L1D cache 
should show a large decrease in performance. I'm using: "RiscvMinorCPU()" with 
"system.mem_mode = 'timing'". Benchmark code should reuse memory within a 24KiB 
block, so the performance between a 32KiB cache and a 1KiB cache should be 
significant.

Call to benchmark code in the C code would look something like 
"ubench_cache(100, buffer, (1<<10)*24);".

static uint32_t ubench_cache(const size_t iters,
                             const void *in,
                             const size_t sz) {
  const uint8_t *buf = (uint8_t*)in;
  const size_t def_blk_sz = ((size_t)(1<<10)) * 24;
  const size_t blk_sz = (sz < def_blk_sz) ? (sz) : (def_blk_sz);
  const size_t cl_sz = 64;
  const size_t in_iters = 100;
  uint8_t h = 0;
  for (size_t j=0; j < iters; j++) {               // Outer iterations
    for (size_t b=0; b < sz; b+=blk_sz) {          // There will be only 1 block
      for (size_t i=0; i < in_iters; i++) {        // Inner iterations
        for (size_t o=0; o < cl_sz; o++) {         // Offset withing a cache 
line
          for (size_t c=0; c < blk_sz; c+=cl_sz) { // Cache line within a block
            const size_t ndx = b + c + o;
            h += (ndx < sz) ? (buf[ndx]) : (i);
          }
        }
      }
    }
  }
  return (uint32_t)h;
}

To have something else to test with, can anyone recommend a small / simple 
cache benchmark written in C? I'm trying to see if my Gem5 configuration is the 
problem, or if this test isn't a good one.

Thanks much,
~Aaron Vose

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