HP Integrity VM Accelerated Virtual I/O Overview

• Lack of I/O performance limits the deployment of virtual machines.
Now let’s look at the accelerated Integrity VM guest driver model. This is the model used by AVIO.
Figure 1 illustrates the modified guest driver model for Integrity VM.
There are three key points to note about this model:
1. No Device Emulation – Device emulation is no longer required. The AVIO guest driver
model uses an Integrity VM-specific programming interface to initiate control and I/O
requests.
2. No protocol driver – the protocol driver is replaced by AVIO host modules that
significantly streamline the processing of I/O requests from the guest.
3. I/O Stack processing – the AVIO guest driver solution enables both storage and
networking to only traverse the I/O stack once (either in the guest or the host, but not both
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).
Benefits of the accelerated Integrity VM guest drivers:
• I/O performance is improved by significantly reducing the I/O path length for I/O request
processing.
• Typically improves the performance of I/O intensive workloads.
• Enables wider deployment of virtual machines.
• Allows easier integration of new server and I/O virtualization capabilities.
Drawbacks of the accelerated Integrity VM guest drivers:
• Requires new guest drivers for each supported OS.
• Verification and support costs are higher.
• Boot/Dump and OS install support are more difficult to integrate across different Operating
Systems (i.e. HP-UX, Windows, Linux, and VMS).
Workload Implications for AVIO LAN
The AVIO networking driver provides significant path length reductions in the host I/O path over the
current emulated LAN solution. In addition, the AVIO guest networking driver supports two key
stateless protocol offload features: TCP Segmentation Offload (TSO) and Checksum Offload (CKO)
that minimize the transitions between the guest and the host driver. TSO and CKO are Ethernet
chipset features that offload TCP Segmentation and Checksum processing from the host processor to
the Ethernet chipset. The combination of these improvements provides significant performance
improvements over the current emulated LAN solution.
In general, AVIO delivers the best performance improvements over the current LAN solution with
streaming applications or workloads. More specifically, when streaming data with average message
sizes of 1K, AVIO delivers 2X or better improvements in bandwidth and 60% or better improvements
in CPU costs for 1GbE.
Applications or workloads that are primarily request-response oriented do not exhibit significant
improvements in performance with AVIO. This is due to the fixed costs introduced each time the guest
crosses the guest to host boundary. It should be noted that this is true of any virtualization solution that
does not provide direct I/O support
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Workload Implications for AVIO Storage
The AVIO storage driver provides about twenty percent path-length reduction compared to the legacy
SCSI driver. The AVIO storage driver also implements adaptive algorithms for minimizing transitions
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AVIO Storage does use the guest I/O SCSI stack for configuration.
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Direct I/O utilizes server I/O hardware (that is, IOMMU) to provide guest isolation and, therefore, the hypervisor is removed from the I/O path
in most cases (the hypervisor still needs to participate in interrupt delivery).