Fix too low cpu_times_percent values when interval < ~1 second (#1586)

Signed-off-by: Frank Kusters <frank.kusters@sioux.eu>

Author: frankkusters

CREDITS

@@ -831,3 +831,6 @@ I: 2376
 N: Anthony Ryan
 W: https://github.com/anthonyryan1
 I: 2272
+
+N: Frank Kusters
+I: 1586

HISTORY.rst

@@ -20,6 +20,9 @@
 
 **Bug fixes**
 
+- 1586_, `cpu_times_percent()`_ reports much too low values if the interval is
+  less than 1 second (with ``percpu=True``) or less than ``1/cpu_count()``
+  seconds (with ``percpu=False``).
 - 2395_, [OpenBSD]: `pid_exists()`_ erroneously return True if the argument is
   a thread ID (TID) instead of a PID (process ID).
 - 2254_, [Linux]: offline cpus raise NotImplementedError in cpu_freq() (patch by Shade Gladden)

psutil/__init__.py

@@ -1846,10 +1846,9 @@ def calculate(t1, t2):
         times_delta = _cpu_times_deltas(t1, t2)
         all_delta = _cpu_tot_time(times_delta)
         # "scale" is the value to multiply each delta with to get percentages.
-        # We use "max" to avoid division by zero (if all_delta is 0, then all
-        # fields are 0 so percentages will be 0 too. all_delta cannot be a
-        # fraction because cpu times are integers)
-        scale = 100.0 / max(1, all_delta)
+        # Avoid division by zero (if all_delta is 0, then all fields are 0 so
+        # percentages will be 0 too).
+        scale = 100.0 / all_delta if all_delta > 0 else 100.0
         for field_delta in times_delta:
             field_perc = field_delta * scale
             field_perc = round(field_perc, 1)