CA-189076: Make sure perfmon wait at least the defined interval

With the current implementation, perfmon's actual idle intervals are between
(defined_value - some_dither) and (defined_value + some_dither). It means that
there are close to 50% cases where the actual idle/waiting periods are smaller
than the defined value.

This triggered an edge cases on alarm generation. When the alarm inhibite
period is the same as perfmon's defined interval (i.e. the 5 min minimum),
there are good chances that many alarms would be deferred until the next
iteration as the inhibit period since last alarm has not fully expired (even
though quite close). In cases where the same alarm should be generated
continuously (at each iteration), the proportion of missing alarms would appear
to be very high.

This change makes sure that the actual waiting interval of perfmon covers at
least the defined value.

Signed-off-by: Zheng Li <[email protected]>

Author: zli

scripts/perfmon

@@ -1154,8 +1154,8 @@ def main():
         # trust GC to do it on its own
         gc.collect()
 
-        # Sleep for interval +/- dither, exiting early if we recv a cmd
-        timeout = rand(interval - dither, interval + dither)
+        # Sleep for interval + dither, exiting early if we recv a cmd
+        timeout = rand(interval, interval + dither)
         cmdsock.settimeout(timeout)
         try:
             cmd = cmdsock.recv(cmdmaxlen)