1 files changed, 67 insertions, 0 deletions
diff --git a/tools/gnuplot/mem_lat.c b/tools/gnuplot/mem_lat.c
new file mode 100644
index 0000000..b85a08f
--- /dev/null
+++ b/tools/gnuplot/mem_lat.c
@@ -0,0 +1,67 @@
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+enum : size_t {
+  KB = 1024,
+  MB = 1024 * KB,
+
+  DFL_MAXSZ  = 64 * MB,
+  DFL_STRIDE = 256,
+  NUM_ACCESS = 1ull << 24,
+};
+
+static inline uint64_t rdtsc() {
+  uint32_t eax, edx;
+  asm volatile("rdtsc" : "=a"(eax), "=d"(edx));
+  return ((uint64_t)edx << 32) | eax;
+}
+
+uint64_t run_one_walk(size_t size, size_t stride) {
+  // Check size is power of two.
+  assert((size & (size -1)) == 0);
+  assert((size / stride) <= NUM_ACCESS);
+
+  unsigned char *mem = (unsigned char *)malloc(size);
+  memset(mem, 0x55, size);
+
+  const uint64_t start = rdtsc();
+  for (size_t it = 0; it < NUM_ACCESS; it++) {
+    ((volatile unsigned char *)mem)[(it * stride) & (size - 1)]++;
+  }
+  const uint64_t stop = rdtsc();
+
+  free(mem);
+  return stop - start;
+}
+
+int main(int argc, char *argv[]) {
+  size_t max_sz = DFL_MAXSZ;
+  size_t stride = DFL_STRIDE;
+
+  if (argc > 1) {
+    max_sz = strtoll(argv[1], 0, 10);
+    max_sz *= MB;
+  }
+  if (argc > 2) {
+    stride = strtoll(argv[2], 0, 10);
+  }
+
+  fprintf(stderr, "max_sz=%zuK stride=%zu access=%zu\n",
+          max_sz / KB, stride, NUM_ACCESS);
+
+  size_t size = 2048;
+  while (size <= max_sz) {
+    uint64_t cycles = 0;
+    for (size_t loop = 0; loop < 10; ++loop) {
+      cycles += run_one_walk(size, stride);
+    }
+    printf("%6zuK %f\n", size / KB, (double)cycles / NUM_ACCESS / 10.0);
+
+    size *= 2;
+  }
+
+  return 0;
+}