Long time of node_submit + node_save I measure time of my batch node creation and it's fairly acceptable at the beginning with, let's say 200 nodes, and totally disappointing at 1700 nodes. After some measurements I found out that the culprit is the node_submit / node_save part. For loop of 20 nodes creation it takes 5-6 seconds for each node to happen. 

Where should I look for optimization? Is it some heavy module ruining my performance? Maybe it's some devel function that slows it down. 

On almost empty base my call runs for 8 secs. When there's about 1600 nodes in the base I have to wait 120 secs! (loop of 20-21 nodes 5 secs each).
I found the culprit. After turning most of the modules I found out it's WORKBENCH.. Probably it has efficiency problems. Now instead of 15-20 seconds it takes 1 sec to node_save.