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HiperSockets

VM Guest LAN support, also in z/VM 4.2.0, provides the capability for a VM guest to define a virtual HiperSocket adapter and connect it with other virtual network adapters on the same VM host system to form an emulated LAN segment. While real HiperSockets support requires a z/800 or z/900, VM Guest LAN support is available on G5 and G6 processors as well.

This section summarizes the results of a performance evaluation of TCP/IP VM comparing the new HiperSockets and Guest LAN support with existing QDIO, IUCV and VCTC support.

Methodology:   An internal tool was used to drive request-response (RR), connect-request-response (CRR) and streaming (S) workloads. The request-response workload consisted of the client sending 200 bytes to the server and the server responding with 1000 bytes. This interaction lasted for 200 seconds. The connect-request-response workload had the client connecting, sending 64 bytes to the server, the server responding with 8K and the client then disconnecting. This same sequence was repeated for 200 seconds. The streaming workload consisted of the client sending 20 bytes to the server and the server responding with 20MB. This sequence was repeated for 400 seconds.

Each workload was run using IUCV, VCTC, HiperSockets, Guest LAN and QDIO connectivity at various MTU sizes. For IUCV, VCTC and QDIO 1500 and 8992 MTU sizes were chosen. For HiperSockets and Guest LAN 8K, 16K, 32K and 56K MTU sizes were used. For HiperSockets, the Maximum Frame Size (MFS) specified on the CHPID definition is also important. The MFS defined for the system were 16K, 24K, 40K and 64K and are associated with MTU sizes of 8K, 16K, 32K and 56K respectively. All measurements included 1, 5, 10, 20 and 50 client-server pairs. The clients and servers ran on the same VM system with a TCPIP stack for the clients and a separate TCPIP stack for the servers.

The measurements were done on a 2064-109 in an LPAR with 2 dedicated processors. The LPAR had 1GB central storage and 2GB expanded storage. APARs VM62938 and PQ51738, which enable HiperSockets support, were applied. CP monitor data was captured during the measurement run, and reduced using VMPRF.

Specifying DATABUFFERLIMITS 10 10 in the TCPIP configuration file helped to increase the throughput. It was also necessary to specify 65536 for DATABUFFERPOOLSIZE and LARGEENVELOPEPOOLSIZE to support the larger MTUs.

Results:   The following charts show, for each workload (RR, CRR and streaming), throughput and CPU time. Each chart has a line for each connectivity/MTU pair measured. Throughput for all cases shows generally the same trend of reaching a plateau and then trailing off. The corresponding CPU time, in general, shows the same pattern where time decreases until the throughput plateau is reached. As throughput trails off, the time increases showing we've passed the optimum point. Specific details are mentioned for each workload after the charts for that workload.

Figure 1. RR Throughput

Figure 2. RR CPU Time

The CPU Time shows that while the legacy connectivity types (IUCV and VCTC) have basically the same time no matter how many client-server pairs are running, the others do gain efficiency as the number of connections increases until about 20 connections.

MTU size doesn't have much effect on throughput because of the small amount of data sent in the RR workload.

IUCV and VCTC have better throughput since they have been optimized for VM-to-VM communication whereas the other connectivity types have to support more than just the VM environment and therefore are not as optimized.

The throughput for all connectivity types plateaus at 10 users.

Figure 3. CRR Throughput

Figure 4. CRR CPU Time

With the CRR workload, IUCV and VCTC have lost their advantage because they are not as efficient with connect and disconnect. The optimization done for moving data does not help as much with this workload.

The CPU times are greater for CRR than RR for the same reason (connect and disconnect overhead).

The plateau is reached between 5 and 10 users, depending on the connectivity type.

Guest LAN handles CRR more efficiently than the other types.

Figure 5. Streaming Throughput

Figure 6. Streaming CPU Time

The number of connections is not as significant for the streaming workload as it was for RR and CRR.

MTU size, however, does make a difference with this workload because of the large amounts of data being transferred. Bigger is better.

An anomaly was noted for the single user Guest LAN case when running with 56K MTU size. This is currently being investigated.

It is possible that IUCV and VCTC may do better than shown in this chart if an MTU size larger than 8992 is chosen.

The throughput and CPU time results for all runs are summarized in the following tables (by connectivity type).

Table 1. Throughput and CPU Time: HiperSockets

Table 2. Throughput and CPU Time: Guest LAN

Table 3. Throughput and CPU Time: QDIO

Table 4. Throughput and CPU Time: IUCV

Table 5. Throughput and CPU Time: VCTC

Maximum Throughput Results:   The maximum throughput for each workload is summarized in the following tables. MB/sec (megabytes per second), trans/sec (transactions per second) and response time were supplied by the workload driver and show the throughput rate. All other values are from CP monitor data or derived from CP monitor data.

Table 6. Maximum Throughput: Request-Response

Both IUCV and vCTC attained 99% CPU utilization for this workload and therefore are gated by the available processors. IUCV had the best throughput with 2116.14 transactions a second.

The driver client virtual machines communicate with the TCPIP2 stack virtual machine. The driver server virtual machines communicate with the TCPIP1 stack virtual machine. All cases show that the driver clients and servers used a large portion of the resources available.

Table 7. Maximum Throughput: Connect-Request-Response

CRR throughput is less than RR throughput due to the overhead of connect/disconnect. Guest LAN seemed to handle the CRR workload the best. The client stack appeared to be the limiting factor in all cases. For all cases 90% of the time or greater the stacks were either running or waiting for the CPU. Since the stack design is based on a uni-processor model, it will never be able to exceed 100% of one processor.

Table 8. Maximum Throughput: Streaming

QDIO was the winner for the streaming workload. For QDIO, total system CPU utilization limited throughput. For HiperSockets and Guest LAN, the client stack was the limiting factor with more than 95% of the time either running or waiting on the CPU.

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