Use 2 second loop smoothing period rather than 20 seconds

Summary: This was accidentally changed in D4375539.

Reviewed By: philippv

Differential Revision: D4393574

fbshipit-source-id: 0420223575bad0c6b0e89f8cf5ed138e063462b9

folly/io/async/EventBase.cpp

@@ -90,7 +90,7 @@ EventBase::EventBase(bool enableTimeMeasurement)
   , queue_(nullptr)
   , fnRunner_(nullptr)
   , maxLatency_(0)
-  , avgLoopTime_(std::chrono::milliseconds(2000000))
+  , avgLoopTime_(std::chrono::seconds(2))
   , maxLatencyLoopTime_(avgLoopTime_)
   , enableTimeMeasurement_(enableTimeMeasurement)
   , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon
@@ -136,7 +136,7 @@ EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
   , queue_(nullptr)
   , fnRunner_(nullptr)
   , maxLatency_(0)
-  , avgLoopTime_(std::chrono::milliseconds(2000000))
+  , avgLoopTime_(std::chrono::seconds(2))
   , maxLatencyLoopTime_(avgLoopTime_)
   , enableTimeMeasurement_(enableTimeMeasurement)
   , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon