With the increasing number of physical cores in a system, the networking bandwidth requirement per server has also increased. We often find many networking-intensive applications are now being placed on a single server, which results in a single vSphere server requiring more than one 10 Gigabit Ethernet (GbE) adapter. Additional network interface cards (NICs) are also deployed to separate management traffic and the actual virtual machine traffic. It is important for these servers to service the connected NICs well and to drive line rate on all the physical adapters simultaneously.
vSphere 5.5 supports eight 10GbE NICs on a single host, and we demonstrate that a host running with vSphere 5.5 can not only drive line rate on all the physical NICs connected to the system, but can do it with a modest increase in overall CPU cost as we add more NICs.
We configured a single host with four dual-port Intel 10GbE adapters for the experiment and connected them back-to-back with an IXIA Application Network Processor Server with eight 10GbE ports to generate traffic. We then measured the send/receive throughput and the corresponding CPU usage of the vSphere host as we increased the number of NICs under test on the system.
- System Under Test: Dell PowerEdge R820
- CPUs: 4 x Intel Xeon Processors E5-4650 @ 2.70GHz
- Memory: 128GB
- NICs:8 x Intel 82599EB 10GbE, SFP+ Network Connection
- Client: Ixia Xcellon-Ultra XT80-V2, 2U Application Network Processor Server
Challenges in Getting 80Gbps Throughput
To drive near 80 gigabits of data per second from a single vSphere host, we used a server that has not only the required CPU and memory resources, but also the PCI bandwidth that can perform the necessary I/O operations. We used a Dell PowerEdge Server with an Intel E5-4650 processor because it belongs to the first generation of Intel processors that supports PCI Gen 3.0. PCI Gen 3.0 doubles the PCI bandwidth capabilities compared to PCI Gen 2.0. Each dual-port Intel 10GbE adapter needs at least a PCI Gen 2.0 x8 to reach line rate. Also, the processor has Intel Data Direct I/O Technology where the packets are placed directly in the processor cache rather than going to the memory. This reduces the memory bandwidth consumption and also helps reduce latency.
Each 10GbE port of the vSphere 5.5 server was configured with a separate vSwitch, and each vSwitch had two Red Hat 6.0 Linux virtual machines running an instance of Apache web server. The web server virtual machines were configured with 1 vCPU and 2GB of memory with VMXNET3 as the virtual NIC adapter. The 10GbE ports were then connected to the Ixia Application Server port. Since the server had two x16 slots and five x8 slots, we used the x8 slots for the four 10GbE NICs so that each physical NIC had identical resources. For each physical connection, we then configured 200 web/HTTP connections, 100 for each web server, on an Ixia server that requested or posted the file. We used a high number of connections so that we had enough networking traffic to keep the physical NIC at 100% utilization.
Figure 1. System design of NICs, switches, and VMs
The Ixia Xcellon application server used an HTTP GET request to generate a send workload for the vSphere host. Each connection requested a 1MB file from the HTTP web server.
Figure 2 shows that we could consistently get the available line rate for each physical NIC as we added more NICs to the test. Each physical NIC was transmitting 120K packets per second and the average TSO packet size was close to 10K. The NIC was also receiving 400K packets per second for acknowledgements on the receive side. The total number of packets processed per second was close to 500K for each physical connection.
Figure 2. vSphere 5.5 drives throughput at available line rates. TSO on the NIC resulted in lower packets per second for send.
Similar to the send case, we configured the application server to post a 1MB file using an HTTP POST request for generating receive traffic for the vSphere host. We used the same number of connections and observed similar behavior for the throughput. Since the NIC does not have support for hardware LRO, we were getting 800K packets per second for each NIC. With eight 10GbE NICs, the packet rate reached close to 6.4 million packets per second. VMware does Software LRO for Linux and as a result we see large packets in the guest. The guest packet rate is around 240K packets per second. There was also significant traffic for TCP acknowledgements and for each physical NIC. The host was transmitting close to 120K acknowledgement packets for each physical NIC, bringing the total packets processed close to 7.5 million packets per second for eight 10Gb ports.
Figure 3. Average vSphere 5.5 host CPU utilization for send and receive
We also measured the average CPU reported for each of the tests. Figure 3 shows that the vSphere host’s CPU usage increased linearly as we added more physical NICs to the test for both send and receive. This indicates that performance improves at an expected and acceptable rate.
Test results show that vSphere 5.5 is an excellent platform on which to deploy networking-intensive workloads. vSphere 5.5 makes use of all the physical bandwidth capacity available and does this without incurring additional CPU cost.
A 10GbE NIC can achieve only 9.4 Gbps of throughput with standard MTU. For a 1500 byte packet, we have 40 bytes for the TCP /IP header and 38 bytes for the Ethernet frame format.