NAME

     ptnet — Ethernet driver for passed-through netmap ports

SYNOPSIS

     This network driver is included in netmap(4), and it can be compiled into the kernel by adding the
     following line in your kernel configuration file:

           device netmap

DESCRIPTION

     The ptnet device driver provides direct access to host netmap ports, from within a Virtual Machine (VM).
     Applications running inside the VM can access the TX/RX rings and buffers of a netmap port that the
     hypervisor has passed-through to the VM.  Hypervisor support for ptnet is currently available for QEMU/KVM.
     Any netmap(4) port can be passed-through, including physical NICs, vale(4) ports, netmap pipes, etc.

     The main use-case for netmap passthrough is Network Function Virtualization (NFV), where middlebox
     applications running within VMs may want to process very high packet rates (e.g., 1-10 millions packets per
     second or more).  Note, however, that those applications must use the device in netmap mode in order to
     achieve such rates.  In addition to the general advantages of netmap, the improved performance of ptnet
     when compared to hypervisor device emulation or paravirtualization (e.g., vtnet(4), vmx(4)) comes from the
     hypervisor being completely bypassed in the data-path.  For example, when using vtnet(4) the VM has to
     convert each mbuf(9) to a VirtIO-specific packet representation and publish that to a VirtIO queue; on the
     hypervisor side, the packet is extracted from the VirtIO queue and converted to a hypervisor-specific
     packet representation.  The overhead of format conversions (and packet copies, in same cases) is not
     incured by ptnet in netmap mode, because mbufs are not used at all, and the packet format is the one
     defined by netmap (e.g., struct netmap_slot) along the whole data-path.  No format conversions or copies
     happen.

     It is also possible to use a ptnet device like a regular network interface, which interacts with the
     FreeBSD network stack (i.e., not in netmap mode).  However, in that case it is necessary to pay the cost of
     data copies between mbufs and netmap buffers, which generally results in lower TCP/UDP performance than
     vtnet(4) or other paravirtualized network devices.  If the passed-through netmap port supports the VirtIO
     network header, ptnet is able to use it, and support TCP/UDP checksum offload (for both transmit and
     receive), TCP segmentation offload (TSO) and TCP large receive offload (LRO).  Currently, vale(4) ports
     support the header.  Note that the VirtIO network header is generally not used in NFV use-cases, because
     middleboxes are not endpoints of TCP/UDP connections.

TUNABLES

     Tunables can be set at the loader(8) prompt before booting the kernel or stored in loader.conf(5).

     dev.netmap.ptnet_vnet_hdr
             This tunable enables (1) or disables (0) the VirtIO network header.  If enabled, ptnet uses the
             same header used by vtnet(4) to exchange offload metadata with the hypervisor.  If disabled, no
             header is prepended to transmitted and received packets.  The metadata is necessary to support
             TCP/UDP checksum offloads, TSO, and LRO.  The default value is 1.

SEE ALSO

     netintro(4), netmap(4), vale(4), virtio(4), vmx(4), ifconfig(8)

HISTORY

     The ptnet driver was written by Vincenzo Maffione <vmaffione@FreeBSD.org>.  It first appeared in
     FreeBSD 12.0.