[BUG] ixgbe: something wrong with queue selection ?

[Eric Dumazet <eric.dumazet@gmail.com>]

Hi guys

I have bad feelings with ixgbe and its multiqueue selection.

On a quad core machine (Q6600), I get lots of reorderings on a single
TCP stream.


Apparently packets happily spread on all available queues, instead of a
single one.

This defeats GRO at receiver and TCP performance is really bad.

# ethtool -S eth5|egrep "x_queue_[0123]_packets" ; taskset 1 netperf -H
192.168.99.1 ; ethtool -S eth5|egrep "x_queue_[0123]_packets"
     tx_queue_0_packets: 24
     tx_queue_1_packets: 26
     tx_queue_2_packets: 32
     tx_queue_3_packets: 16
     rx_queue_0_packets: 11
     rx_queue_1_packets: 47
     rx_queue_2_packets: 27
     rx_queue_3_packets: 22
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.99.1 (192.168.99.1) port 0 AF_INET
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 87380  16384  16384    10.00    3866.43   
     tx_queue_0_packets: 1653201
     tx_queue_1_packets: 608000
     tx_queue_2_packets: 541382
     tx_queue_3_packets: 536543
     rx_queue_0_packets: 434703
     rx_queue_1_packets: 137444
     rx_queue_2_packets: 131023
     rx_queue_3_packets: 128407

# ip ro get 192.168.99.1
192.168.99.1 dev eth5  src 192.168.99.2 
    cache  ipid 0x438b rtt 4ms rttvar 4ms cwnd 57 reordering 127

# lspci -v -s 02:00.0
02:00.0 Ethernet controller: Intel Corporation 82599EB 10-Gigabit
SFI/SFP+ Network Connection (rev 01)
	Subsystem: Intel Corporation Ethernet Server Adapter X520-2
	Flags: bus master, fast devsel, latency 0, IRQ 16
	Memory at f1100000 (64-bit, prefetchable) [size=512K]
	I/O ports at b000 [size=32]
	Memory at f1200000 (64-bit, prefetchable) [size=16K]
	Capabilities: [40] Power Management version 3
	Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
	Capabilities: [70] MSI-X: Enable+ Count=64 Masked-
	Capabilities: [a0] Express Endpoint, MSI 00
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Device Serial Number 00-1b-21-ff-ff-4a-fe-54
	Capabilities: [150] Alternative Routing-ID Interpretation (ARI)
	Capabilities: [160] Single Root I/O Virtualization (SR-IOV)
	Kernel driver in use: ixgbe
	Kernel modules: ixgbe