benchmarking: correct for differences in CPU and TSC frequency

1 files changed, 23 insertions, 0 deletions

diff --git a/etc/tscfreq.c b/etc/tscfreq.c
new file mode 100644
index 000000000..459db083c
--- /dev/null
+++ b/etc/tscfreq.c
@@ -0,0 +1,23 @@
+#include <unistd.h>
+#include <stdio.h>
+
+// cpucycles_amd64cpuinfo
+long long cpucycles(void)
+{
+  unsigned long long result;
+  asm volatile(".byte 15;.byte 49;shlq $32,%%rdx;orq %%rdx,%%rax"
+    : "=a" (result) ::  "%rdx");
+  return result;
+}
+
+static const long long usecs = 100*1000;
+
+int main() {
+  long long t0 = cpucycles();
+  usleep(usecs);
+  long long t1 = cpucycles();
+  const long long tsc_hz  = ((t1-t0)*1000*1000)/usecs;
+  const long long tsc_mhz = tsc_hz / 1000 / 1000;
+  const long long tsc_ghz = tsc_mhz / 1000;
+  printf("%1d.%02d\n", tsc_ghz, (tsc_mhz - 1000*tsc_ghz + 5)/10);
+}