All Indexers were upgraded to Splunk 6.0.1. however, the response time from the master head 6.0.1 continues to be slower compared to splunk 5.0.2 master head.
For the sake of clarity, both master heads are running with the same type of hardware.
Open case with splunk tech support.
Remote timeline feature can reduce performance
A 6.x search head by default asks its search peers to generate a remote timeline. This isn't a problem with 6.x search peers, but 5.x search peers won't know how to generate the timeline. As a result, searches can slow dramatically.
The workaround is to add the following attribute to limits.conf on the search head :
remote_timeline_fetchall = false
After making this change, you must restart the search head.
Important: You should remove this attribute after all search peers have been upgraded to 6.x.