Hi Thomas,
The switch and the adapter, both have xon and xoff thresholds (when to send the "pause sending" or the "continue sending" messages. The threshold numbers are designed in a way to be able to absorb the traffic from the time you send the pause frame, until it actually stops.
In other words, once you enable Flow control globally on the port, you should not have any drops on the link.
Thanks,
Ophir.