24. GVE poll mode driver

The GVE PMD (librte_net_gve) provides poll mode driver support for Google Virtual Ethernet device (also called as gVNIC).

gVNIC is the standard virtual Ethernet interface on Google Cloud Platform (GCP), which is one of the multiple virtual interfaces from those leading CSP customers in the world.

Please refer to https://cloud.google.com/compute/docs/networking/using-gvnic for the device description.

Having a well maintained/optimized gve PMD on DPDK community can help those cloud instance consumers with better experience of performance, maintenance who wants to run their own VNFs on GCP.

The base code is under MIT license and based on GVE kernel driver v1.3.0. GVE base code files are:

  • gve_adminq.h
  • gve_adminq.c
  • gve_desc.h
  • gve_desc_dqo.h
  • gve_register.h
  • gve.h

Please refer to https://github.com/GoogleCloudPlatform/compute-virtual-ethernet-linux/tree/v1.3.0/google/gve to find the original base code.

GVE has 3 queue formats:

  • GQI_QPL - GQI with queue page list
  • GQI_RDA - GQI with raw DMA addressing
  • DQO_RDA - DQO with raw DMA addressing

GQI_QPL queue format is queue page list mode. Driver needs to allocate memory and register this memory as a Queue Page List (QPL) in hardware (Google Hypervisor/GVE Backend) first. Each queue has its own QPL. Then Tx needs to copy packets to QPL memory and put this packet’s offset in the QPL memory into hardware descriptors so that hardware can get the packets data. And Rx needs to read descriptors of offset in QPL to get QPL address and copy packets from the address to get real packets data.

GQI_RDA queue format works like usual NICs that driver can put packets’ physical address into hardware descriptors.

DQO_RDA queue format has submission and completion queue pair for each Tx/Rx queue. And similar as GQI_RDA, driver can put packets’ physical address into hardware descriptors.

Please refer to https://www.kernel.org/doc/html/latest/networking/device_drivers/ethernet/google/gve.html to get more information about GVE queue formats.

24.1. Features and Limitations

In this release, the GVE PMD provides the basic functionality of packet reception and transmission. Supported features of the GVE PMD are:

  • Multiple queues for Tx and Rx
  • TSO offload
  • Link state information
  • Tx multi-segments (Scatter Tx)
  • Tx UDP/TCP/SCTP Checksum
  • RSS hash configuration
  • RSS redirection table query and update

Currently, only GQI_QPL and GQI_RDA queue format are supported in PMD. Jumbo Frame is not supported in PMD for now. It’ll be added in a future DPDK release. Also, only GQI_QPL queue format is in use on GCP since GQI_RDA hasn’t been released in production.

24.1.1. RSS

GVE RSS can be enabled and configured using the standard interfaces. The driver does not support querying the initial RSS configuration.

The RSS hash key must be exactly 40 bytes. Upon RSS hash configuration, a default redirection table will be set using a round-robin assignment of hash values to queues. The default GVE redirection table has 128 entries.

Note that the initial configuration requires a hash key to be provided if one had not been provided before. Attempting to set hash types alone without the existence of a set key will result in a failed request.

As stated above, the RSS redirection table has exactly 128 entries. The RSS hash must be configured before the redirection table can be updated using the standard interface. Because the initial RSS hash creates a default redirection table, the redirection table will be available for querying upon initial hash configuration. When performing redirection table updates, it is possible to update individual table entries.