Chelsio Communications Chelsio T4, Installation And User Manual

Page: 57 / 511

Chapter II. Network (NIC/TOE)
Chelsio T5/T4 Unified Wire for Linux
Page 57
[root@receiver_host~]# iperf –s
Then on the sender host, send data to the server using the iperf client mode. To emulate a
moderate traffic workload, use
-P option to request 20 TCP streams from the server:
[root@sender_host~]# iperf -c receiver_host_name_or_IP -P 20
Then on the receiver host, look at interrupt rate at /proc/interrupts :
[root@receiver_host~]# cat /proc/interrupts | grep eth6
Id CPU0 CPU1 CPU2 CPU3 type interface
36: 115229 0 0 1 PCI-MSI-edge eth6 (queue 0)
37: 0 121083 1 0 PCI-MSI-edge eth6 (queue 1)
38: 0 0 105423 1 PCI-MSI-edge eth6 (queue 2)
39: 0 0 0 115724 PCI-MSI-edge eth6 (queue 3)
Now interrupts from eth6 are evenly distributed among the 4 CPUs.
Without T5/T4’s RSS support, the interrupts caused by network traffic may be distributed
unevenly over CPUs. For your information, the traffic produced by the same iperf commands
gives the following output in
/proc/interrupts .
[root@receiver_host~]# cat /proc/interrupts | grep eth6
Id CPU0 CPU1 CPU2 CPU3 type interface
36: 0 9 0 17418 PCI-MSI-edge eth6 (queue 0)
37: 0 0 21718 2063 PCI-MSI-edge eth6 (queue 1)
38: 0 7 391519 222 PCI-MSI-edge eth6 (queue 2)
39: 1 0 33 17798 PCI-MSI-edge eth6 (queue 3)
Here there are 4 receiving queues from the eth6 interface, but they are not bound to a specific
CPU or interrupt entry. Queue 2 has caused a very large number of interrupts on CPU2 while
CPU0 and CPU1 are barely used by any of the four queues. Enabling RSS is thus essential for
best performance.