bench_sleep0.py: dynamically select N; measure cpu time

greentest/bench_sleep0.py

 from time import time
 from gevent import sleep
+import os
 
-N = 10000
 
+N = 10
 
-start = time()
-for _ in xrange(N):
-    sleep(0)
-delta = time() - start
-print ('sleep(0): %.1f microseconds' % (delta * 1000000.0 / N))
+
+while True:
+    start = time()
+    user_time, system_time = os.times()[:2]
+    for _ in xrange(N):
+        sleep(0)
+    user_time_x, system_time_x = os.times()[:2]
+    delta = time() - start
+    if delta > 1:
+        break
+    N *= 10
+user_time_x -= user_time
+system_time_x -= system_time
+ms = 1000000. / N
+print 'N=%s delta=%s utime=%s stime=%s' % (N, delta, user_time_x, system_time_x)
+print ('sleep(0): %.1f, utime: %.1f, stime: %.1f (microseconds)' % (delta * ms, user_time_x * ms, system_time_x * ms))