PX Deq Credit: Send blkd top most wait event in AWR

Hello Gurus,

I have collected AWR report for peak hours snapshots (3 hrs), and following is the TOP 5 Timed Events:

Event	Waits	Time(s)	Avg Wait(ms)	% Total Call Time	Wait Class
PX Deq Credit: Send blkd	20,123	13,991	695	39.8	other
CPU Time		11,778		33.5
df file sequential read	728,444	3,607	5	10.3	User I/O
db file scattered read	797,421	2,447	3	7	User I/O
log file parallel write	19,960	295	15	0.8	System I/O

The top most wait event is PX Deq Credit: Send blkd. I gone through some of the oracle documents which says that this type of wait event is normal even though it is the top most  event in AWR. But other docs specifies that not in all situations this is normal. I just know that this wait event is related to Parallel Processing.