Forgot one thing: please post output of vmstat -i, before/after the RX choking :-)
Here is the same info from FreeBSD Current, post testing. The same hardware does not wedge on it.
em0: Excessive collisions = 0 em0: Symbol errors = 0 em0: Sequence errors = 0 em0: Defer count = 0 em0: Missed Packets = 4188922 em0: Receive No Buffers = 201 em0: Receive Length Errors = 0 em0: Receive errors = 0 em0: Crc errors = 0 em0: Alignment errors = 0 em0: Carrier extension errors = 0 em0: RX overruns = 89594 em0: watchdog timeouts = 0 em0: XON Rcvd = 0 em0: XON Xmtd = 89602 em0: XOFF Rcvd = 0 em0: XOFF Xmtd = 4278524 em0: Good Packets Rcvd = 200185794 em0: Good Packets Xmtd = 13 em0: TSO Contexts Xmtd = 0 em0: TSO Contexts Failed = 0 em0: Adapter hardware address = 0xc4da1948 em0: CTRL = 0x580c0241 RCTL = 0x8002 em0: Packet buffer = Tx=16k Rx=32k em0: Flow control watermarks high = 30720 low = 29220 em0: tx_int_delay = 66, tx_abs_int_delay = 66 em0: rx_int_delay = 0, rx_abs_int_delay = 66 em0: fifo workaround = 0, fifo_reset_count = 0 em0: hw tdh = 25, hw tdt = 25 em0: Num Tx descriptors avail = 256 em0: Tx Descriptors not avail1 = 0 em0: Tx Descriptors not avail2 = 0 em0: Std mbuf failed = 0 em0: Std mbuf cluster failed = 0 em1: CTRL = 0x580c0241 RCTL = 0x8002 em1: Packet buffer = Tx=16k Rx=32k em1: Flow control watermarks high = 30720 low = 29220 em1: tx_int_delay = 66, tx_abs_int_delay = 66 em1: rx_int_delay = 0, rx_abs_int_delay = 66 em1: fifo workaround = 0, fifo_reset_count = 0 em1: hw tdh = 26, hw tdt = 26 em1: Num Tx descriptors avail = 256 em1: Tx Descriptors not avail1 = 0 em1: Tx Descriptors not avail2 = 0 em1: Std mbuf failed = 0 em1: Std mbuf cluster failed = 0 em1: Excessive collisions = 0 em1: Symbol errors = 0 em1: Sequence errors = 0 em1: Defer count = 0 em1: Missed Packets = 0 em1: Receive No Buffers = 0 em1: Receive Length Errors = 0 em1: Receive errors = 0 em1: Crc errors = 0 em1: Alignment errors = 0 em1: Carrier extension errors = 0 em1: RX overruns = 0 em1: watchdog timeouts = 0 em1: XON Rcvd = 0 em1: XON Xmtd = 0 em1: XOFF Rcvd = 0 em1: XOFF Xmtd = 0 em1: Good Packets Rcvd = 1 em1: Good Packets Xmtd = 122327310 em1: TSO Contexts Xmtd = 0 em1: TSO Contexts Failed = 0
