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Enabling, disabling, and updating VMMQ on a VPort

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After creating a VPort, an upper layer driver can enable, disable, or update the RSS parameters of the VPort.

The driver can update the RSS indirection table of the VPort in order to change the number queues for a VPort. However the RSS hash type, hash function, and hash secret key of a VPort are considered static parameters and are not changed by the overlying drivers during the lifetime of a VPort. If an upper layer driver wishes to change any of the RSS static parameters, it must delete and recreate the VPort.

The upper layer driver enables, disables, or changes the RSS parameters of a VPort by issuing an OID_GEN_RECEIVE_SCALE_PARAMETERS OID request. The upper layer driver sets the VPortId field in the NDIS_OID_REQUEST structure to the ID of the target VPort of the new configuration.

The upper layer driver also sets the NDIS_RECEIVE_SCALE_PARAMETERS structure used in the OID request as follows. Please note that based on the VMMQ capabilities advertised by the underlying miniport adapter, some of the fields may be set to the same value for all PF VPorts.

  • Set the Revision member of Header to NDIS_RECEIVE_SCALE_PARAMETERS_REVISION_3.

  • Set the NDIS_RSS_PARAM_FLAG_DEFAULT_PROCESSOR_UNCHANGED flag to specify that the DefaultProcessorNumber member has not changed.

  • Set BaseCpuNumber to zero.

  • Set DefaultProcessorNumber to specify the default RSS processor for this VPort. The miniport can assume that default processor is part of RSS processor list, but it cannot assume that the default RSS processor is in the current indirection table.

  • Set HashInformation to indicate the hash type and hash function that the NIC should use to calculate the hash value of the packets received for this VPort. The upper layer driver may set this field to a different value for each VPort.

  • Set IndirectionTableSize to specify the size of the indirection table in bytes. Set this field to the same value for all PF VPorts. The upper layer driver must ensure that the number of entries in the indirection table is a power of two.

  • Set IndirectionTableOffset to specify the offset of the indirection table from the beginning of the NDIS_RECEIVE_SCALE_PARAMETERS structure.

  • Set HashSecretKeySize to specify the size of the hash secret key in bytes. The upper layer driver may set a different secret key for each VPort if the miniport adapter supports this. For more information, see Advertising VMMQ capabilities.

  • Set HashSecretKeyOffset to specify the offset of the hash secret key from the beginning of the NDIS_RECEIVE_SCALE_PARAMETERS structure. The upper layer driver may set a different secret key for each VPort if the miniport adapter supports this. For more information, see Advertising VMMQ capabilities.

  • Set ProcessorMaskOffset, NumberOfProcessorMasks, and ProcessorMasksEntrySize appropriately.

When a miniport driver receives an OID request to disable VMMQ for a VPort, it should revert to indicating all packets received for that VPort on the processor specified by the ProcessorAffinity field in the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure that was used in the OID_NIC_SWITCH_CREATE_VPORT OID request.

Changing the number of queues for a VPort

The number of unique processors used in the indirection table of a VPort cannot exceed the value of the NumQueuePairs field of the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure specified in the last issued OID_NIC_SWITCH_CREATE_VPORT OID request. These processors will be a subset of the RSS processor set returned by a call to NdisGetRssProcessorInformation. For more information, see Allocating VPorts for VMMQ. However, the indirection tables on different VPorts could contain the same processor.

To decrease the number of queues for a PF VPort an upper layer driver must:

  1. Send an OID_GEN_RECEIVE_SCALE_PARAMETERS OID with the original indirection table size. However, the indirection table at this step can only reference the number of distinct processors up to the new number of queues. If the new indirection table needs to be smaller than the original table due to the NDIS_NIC_SWITCH_CAPS_RSS_PER_PF_VPORT_INDIRECTION_TABLE_SIZE_RESTRICTED flag of the NDIS_NIC_SWITCH_PARAMETERS structure, the issuer must guarantee that the indirection table at this step will contain the new indirection table replicated as many times as needed to satisfy the RESTRICTED flag requirement for the original number of queues.

  2. Send an OID_NIC_SWITCH_VPORT_PARAMETERS OID with new number of queues.

  3. Send an OID_GEN_RECEIVE_SCALE_PARAMETERS with the new indirection table size if it has changed.

To increase the number of queues for a PF VPort an upper layer driver must:

  1. The driver doesn't need to update the current indirection table before step 2 because the table only references the number of distinct processors up to the current number of queues.

  2. Send an OID_NIC_SWITCH_VPORT_PARAMETERS OID with new number of queues. If the RESTRICTED flag is set, the miniport driver should internally replicate the original indirection table as many times as needed to match the indirection table size requirement for the new number of queues.

  3. Send an OID_GEN_RECEIVE_SCALE_PARAMETERS OID with new indirection table size if it has changed.