From category "Damn you, WiFi!"...

I just spent the whole workday debugging why my upload was so slow from some devices in my research testbed. One notebook got 100-120 Mbit/s, the others got only 40 Mbit/s.
All used iperf with the same parameters, UDP to the same Access Point (first hop), same channel (40 MHz wide, otherwise empty, on 5 GHz spectrum), all used 802.11n with 2 spatial streams, same driver.
The faster notebook sent way more packets than the others.

Guess why?
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