How to debug throughput issues?

Hi All, I’ve two Bluetooth dongles and connected to two Linux systems(hostname1, hostname2). I’ve a test executable and it creates a BT link does the file transfer and calculates the throughput. I repeated the same test with the same BT dongles on another different Linux systems(hostname3, hostname4), here I’m getting less data rate. Here first I want to narrow down whether the issue is below device driver level or above device driver level and where the bottleneck is? which tools will help me to debug this kind of issue? Thanks