get cpu frequency

README.md

@@ -8,9 +8,14 @@ Usage
 =====
 
 ```python
+import time
 import rdtsc
 
 start = rdtsc.get_cycles()
 # do stuff
+time.sleep(5)
 end = rdtsc.get_cycles()
+frequency = rdtsc.get_cpu_frequency()
+
+print((end - start)/(frequency * 10 ** 6))
 ```

src/rdtsc.c

@@ -1,14 +1,58 @@
+#include <unistd.h>
+#include <sys/time.h>
+
 extern unsigned long long get_cycles()
 {
     long long out;
     asm volatile(
-        "RDTSCP;"  /* outputs to EDX:EAX and the (unused) cpuid to ECX*/
-        "SHLQ $32,%%rdx;"
-        "ORQ %%rdx,%%rax;"
-        "MOVQ %%rax,%0;"
-        :"=r"(out)
-        : /*no input*/
-        :"rdx","rax", "rcx"
-    );
+            "RDTSCP;"  /* outputs to EDX:EAX and the (unused) cpuid to ECX*/
+            "SHLQ $32,%%rdx;"
+            "ORQ %%rdx,%%rax;"
+            "MOVQ %%rax,%0;"
+            :"=r"(out)
+            : /*no input*/
+            :"rdx","rax", "rcx"
+            );
     return out;
 }
+
+/**
+ * Get time delta in microseconds.
+ */
+static long get_us_interval(struct timeval *start, struct timeval *end) {
+    return (((end->tv_sec - start->tv_sec) * 1000000)
+            + (end->tv_usec - start->tv_usec));
+}
+
+/**
+ * This is a microbenchmark to get cpu frequency the process is running on. The
+ * returned value is used to convert TSC counter values to microseconds.
+ *
+ * @return double.
+ * @author cjiang
+ *
+ * see https://github.com/FriendsOfPHP/uprofiler
+ */
+extern double get_cpu_frequency() {
+    struct timeval start;
+    struct timeval end;
+    long long tsc_start;
+    long long tsc_end;
+
+    if (gettimeofday(&start, 0)) {
+        return 0.0;
+    }
+
+    tsc_start = get_cycles();
+
+    /* Sleep for 5 miliseconds. Comparaing with gettimeofday's few microseconds
+     * execution time, this should be enough. */
+    usleep(5000);
+    if (gettimeofday(&end, 0)) {
+        return 0.0;
+    }
+
+    tsc_end = get_cycles();
+
+    return (tsc_end - tsc_start) * 1.0 / (get_us_interval(&start, &end));
+}

src/rdtsc/__init__.py

@@ -23,3 +23,7 @@
 get_cycles = so.get_cycles
 get_cycles.argtypes = []
 get_cycles.restype = ctypes.c_ulonglong
+
+get_cpu_frequency = so.get_cpu_frequency
+get_cpu_frequency.argtypes = []
+get_cpu_frequency.restype = ctypes.c_double