32. Memif Poll Mode Driver
Shared memory packet interface (memif) PMD allows for DPDK and any other client using memif (DPDK, VPP, libmemif) to communicate using shared memory. Memif is Linux only.
The created device transmits packets in a raw format. It can be used with Ethernet mode, IP mode, or Punt/Inject. At this moment, only Ethernet mode is supported in DPDK memif implementation.
Memif works in two roles: master and slave. Slave connects to master over an
existing socket. It is also a producer of shared memory file and initializes
the shared memory. Each interface can be connected to one peer interface
at same time. The peer interface is identified by id parameter. Master
creates the socket and listens for any slave connection requests. The socket
may already exist on the system. Be sure to remove any such sockets, if you
are creating a master interface, or you will see an “Address already in use”
rte_pmd_memif_remove(), which removes memif interface,
will also remove a listener socket, if it is not being used by any other
The method to enable one or more interfaces is to use the
--vdev=net_memif0 option on the DPDK application command line. Each
--vdev=net_memif1 option given will create an interface named net_memif0,
net_memif1, and so on. Memif uses unix domain socket to transmit control
messages. Each memif has a unique id per socket. This id is used to identify
peer interface. If you are connecting multiple
interfaces using same socket, be sure to specify unique ids
etc. Note that if you assign a socket to a master interface it becomes a
listener socket. Listener socket can not be used by a slave interface on same
|Used to identify peer interface
|Set memif role
|Size of single packet buffer
|Log2 of ring size. If rsize is 10, actual ring size is 1024
|string len 108
|Secret is an optional security option, which if specified, must be matched by peer
|string len 24
|Enable/disable zero-copy slave mode. Only relevant to slave, requires ‘–single-file-segments’ eal argument
In order to create memif connection, two memif interfaces, each in separate
process, are needed. One interface in
master role and other in
slave role. It is not possible to connect two interfaces in a single
process. Each interface can be connected to one interface at same time,
identified by matching id parameter.
Memif driver uses unix domain socket to exchange required information between
memif interfaces. Socket file path is specified at interface creation see
Memif configuration options table above. If socket is used by
interface, it’s marked as listener socket (in scope of current process) and
listens to connection requests from other processes. One socket can be used by
multiple interfaces. One process can have
at the same time, provided each role is assigned unique socket.
For detailed information on memif control messages, see: net/memif/memif.h.
Slave interface attempts to make a connection on assigned socket. Process
listening on this socket will extract the connection request and create a new
connected socket (control channel). Then it sends the ‘hello’ message
MEMIF_MSG_TYPE_HELLO), containing configuration boundaries. Slave interface
adjusts its configuration accordingly, and sends ‘init’ message
MEMIF_MSG_TYPE_INIT). This message among others contains interface id. Driver
uses this id to find master interface, and assigns the control channel to this
interface. If such interface is found, ‘ack’ message (
sent. Slave interface sends ‘add region’ message (
every region allocated. Master responds to each of these messages with ‘ack’
message. Same behavior applies to rings. Slave sends ‘add ring’ message
MEMIF_MSG_TYPE_ADD_RING) for every initialized ring. Master again responds to
each message with ‘ack’ message. To finalize the connection, slave interface
sends ‘connect’ message (
MEMIF_MSG_TYPE_CONNECT). Upon receiving this message
master maps regions to its address space, initializes rings and responds with
‘connected’ message (
MEMIF_MSG_TYPE_DISCONNECT) can be sent by both master and slave interfaces at
any time, due to driver error or if the interface is being deleted.
- net/memif/memif.h - control messages definitions
32.2. Zero-copy slave
Zero-copy slave can be enabled with memif configuration option ‘zero-copy=yes’. This option is only relevant to slave and requires eal argument ‘–single-file-segments’. This limitation is in place, because it is too expensive to identify memseg for each packet buffer, resulting in worse performance than with zero-copy disabled. With single file segments we can calculate offset from the beginning of the file for each packet buffer.
Shared memory format
Region 0 is created by memif driver and contains rings. Slave interface exposes DPDK memory (memseg). Instead of using memfd_create() to create new shared file, existing memsegs are used. Master interface functions the same as with zero-copy disabled.
Buffers are dequeued and enqueued as needed. Offset descriptor field is calculated at tx. Only single file segments mode (EAL option –single-file-segments) is supported, as calculating offset from multiple segments is too expensive.
32.2.1. Example: testpmd
In this example we run two instances of testpmd application and transmit packets over memif.
#./build/app/testpmd -l 0-1 --proc-type=primary --file-prefix=pmd1 --vdev=net_memif,role=master -- -i
slave interface (master must be already running so the slave will connect):
#./build/app/testpmd -l 2-3 --proc-type=primary --file-prefix=pmd2 --vdev=net_memif -- -i
You can also enable
#./build/app/testpmd -l 2-3 --proc-type=primary --file-prefix=pmd2 --vdev=net_memif,zero-copy=yes --single-file-segments -- -i
Start forwarding packets:
testpmd> start tx_first
testpmd> show port stats 0
For more details on testpmd please refer to Testpmd Application User Guide.
32.2.2. Example: testpmd and VPP
For information on how to get and run VPP please see https://wiki.fd.io/view/VPP.
Start VPP in interactive mode (should be by default). Create memif master interface in VPP:
vpp# create interface memif id 0 master no-zero-copy
vpp# set interface state memif0/0 up
vpp# set interface ip address memif0/0 192.168.1.1/24
To see socket filename use show memif command:
vpp# show memif
id listener filename
0 yes (1) /run/vpp/memif.sock
Now create memif interface by running testpmd with these command line options:
#./testpmd --vdev=net_memif,socket=/run/vpp/memif.sock -- -i
Testpmd should now create memif slave interface and try to connect to master. In testpmd set forward option to icmpecho and start forwarding:
testpmd> set fwd icmpecho
Send ping from VPP:
vpp# ping 192.168.1.2
64 bytes from 192.168.1.2: icmp_seq=2 ttl=254 time=36.2918 ms
64 bytes from 192.168.1.2: icmp_seq=3 ttl=254 time=23.3927 ms
64 bytes from 192.168.1.2: icmp_seq=4 ttl=254 time=24.2975 ms
64 bytes from 192.168.1.2: icmp_seq=5 ttl=254 time=17.7049 ms