adrv9361 RX sample rate

Hi , 

I'm using the ad9361-iiostream.c example .

I've changed the sample rate to 5Msps with 1Msp buffer size and expected to get at least 5 "buffer_refill"s every 1 second.

Unfortunately i get only 2 buffer refills every second (~2.5Msps).

Actually no matter what sample rate i'm using i get 2.5Msps max.

Any idea what's wrong ? 

Thank you ,

Nimrod