NETMAP(4) FreeBSD Kernel Interfaces Manual NETMAP(4)
NAME
netmap - a framework for fast packet I/O
SYNOPSIS
device netmap
DESCRIPTION
netmap is a framework for extremely fast and efficient packet I/O for
userspace and kernel clients, and for Virtual Machines. It runs on
FreeBSD, Linux and some versions of Windows, and supports a variety of
netmap ports, including
physical NIC ports
to access individual queues of network interfaces;
host ports
to inject packets into the host stack;
VALE ports
implementing a very fast and modular in-kernel software
switch/dataplane;
netmap pipes
a shared memory packet transport channel;
netmap monitors
a mechanism similar to bpf(4) to capture traffic
All these netmap ports are accessed interchangeably with the same API,
and are at least one order of magnitude faster than standard OS
mechanisms (sockets, bpf, tun/tap interfaces, native switches, pipes).
With suitably fast hardware (NICs, PCIe buses, CPUs), packet I/O using
netmap on supported NICs reaches 14.88 million packets per second (Mpps)
with much less than one core on 10 Gbit/s NICs; 35-40 Mpps on 40 Gbit/s
NICs (limited by the hardware); about 20 Mpps per core for VALE ports;
and over 100 Mpps for netmap pipes. NICs without native netmap support
can still use the API in emulated mode, which uses unmodified device
drivers and is 3-5 times faster than bpf(4) or raw sockets.
Userspace clients can dynamically switch NICs into netmap mode and send
and receive raw packets through memory mapped buffers. Similarly, VALE
switch instances and ports, netmap pipes and netmap monitors can be
created dynamically, providing high speed packet I/O between processes,
virtual machines, NICs and the host stack.
netmap supports both non-blocking I/O through ioctl(2), synchronization
and blocking I/O through a file descriptor and standard OS mechanisms
such as select(2), poll(2), kqueue(2) and epoll(7). All types of netmap
ports and the VALE switch are implemented by a single kernel module,
which also emulates the netmap API over standard drivers. For best
performance, netmap requires native support in device drivers. A list of
such devices is at the end of this document.
In the rest of this (long) manual page we document various aspects of the
netmap and VALE architecture, features and usage.
ARCHITECTURE
netmap supports raw packet I/O through a port, which can be connected to
a physical interface (NIC), to the host stack, or to a VALE switch.
Ports use preallocated circular queues of buffers (rings) residing in an
mmapped region. There is one ring for each transmit/receive queue of a
NIC or virtual port. An additional ring pair connects to the host stack.
After binding a file descriptor to a port, a netmap client can send or
receive packets in batches through the rings, and possibly implement
zero-copy forwarding between ports.
All NICs operating in netmap mode use the same memory region, accessible
to all processes who own /dev/netmap file descriptors bound to NICs.
Independent VALE and netmap pipe ports by default use separate memory
regions, but can be independently configured to share memory.
ENTERING AND EXITING NETMAP MODE
The following section describes the system calls to create and control
netmap ports (including VALE and netmap pipe ports). Simpler, higher
level functions are described in the LIBRARIES section.
Ports and rings are created and controlled through a file descriptor,
created by opening a special device
fd = open("/dev/netmap");
and then bound to a specific port with an
ioctl(fd, NIOCREGIF, (struct nmreq *)arg);
netmap has multiple modes of operation controlled by the struct nmreq
argument. arg.nr_name specifies the netmap port name, as follows:
OS network interface name (e.g., 'em0', 'eth1', ...)
the data path of the NIC is disconnected from the host stack, and
the file descriptor is bound to the NIC (one or all queues), or to
the host stack;
valeSSS:PPP
the file descriptor is bound to port PPP of VALE switch SSS.
Switch instances and ports are dynamically created if necessary.
Both SSS and PPP have the form [0-9a-zA-Z_]+ , the string cannot
exceed IFNAMSIZ characters, and PPP cannot be the name of any
existing OS network interface.
On return, arg indicates the size of the shared memory region, and the
number, size and location of all the netmap data structures, which can be
accessed by mmapping the memory
char *mem = mmap(0, arg.nr_memsize, fd);
Non-blocking I/O is done with special ioctl(2) select(2) and poll(2) on
the file descriptor permit blocking I/O.
While a NIC is in netmap mode, the OS will still believe the interface is
up and running. OS-generated packets for that NIC end up into a netmap
ring, and another ring is used to send packets into the OS network stack.
A close(2) on the file descriptor removes the binding, and returns the
NIC to normal mode (reconnecting the data path to the host stack), or
destroys the virtual port.
DATA STRUCTURES
The data structures in the mmapped memory region are detailed in
<sys/net/netmap.h>, which is the ultimate reference for the netmap API.
The main structures and fields are indicated below:
struct netmap_if (one per interface)
struct netmap_if {
...
const uint32_t ni_flags; /* properties */
...
const uint32_t ni_tx_rings; /* NIC tx rings */
const uint32_t ni_rx_rings; /* NIC rx rings */
uint32_t ni_bufs_head; /* head of extra bufs list */
...
};
Indicates the number of available rings (struct netmap_rings) and
their position in the mmapped region. The number of tx and rx rings
(ni_tx_rings, ni_rx_rings) normally depends on the hardware. NICs
also have an extra tx/rx ring pair connected to the host stack.
NIOCREGIF can also request additional unbound buffers in the same
memory space, to be used as temporary storage for packets. The
number of extra buffers is specified in the arg.nr_arg3 field. On
success, the kernel writes back to arg.nr_arg3 the number of extra
buffers actually allocated (they may be less than the amount
requested if the memory space ran out of buffers). ni_bufs_head
contains the index of the first of these extra buffers, which are
connected in a list (the first uint32_t of each buffer being the
index of the next buffer in the list). A 0 indicates the end of the
list. The application is free to modify this list and use the
buffers (i.e., binding them to the slots of a netmap ring). When
closing the netmap file descriptor, the kernel frees the buffers
contained in the list pointed by ni_bufs_head , irrespectively of
the buffers originally provided by the kernel on NIOCREGIF.
struct netmap_ring (one per ring)
struct netmap_ring {
...
const uint32_t num_slots; /* slots in each ring */
const uint32_t nr_buf_size; /* size of each buffer */
...
uint32_t head; /* (u) first buf owned by user */
uint32_t cur; /* (u) wakeup position */
const uint32_t tail; /* (k) first buf owned by kernel */
...
uint32_t flags;
struct timeval ts; /* (k) time of last rxsync() */
...
struct netmap_slot slot[0]; /* array of slots */
}
Implements transmit and receive rings, with read/write pointers,
metadata and an array of slots describing the buffers.
struct netmap_slot (one per buffer)
struct netmap_slot {
uint32_t buf_idx; /* buffer index */
uint16_t len; /* packet length */
uint16_t flags; /* buf changed, etc. */
uint64_t ptr; /* address for indirect buffers */
};
Describes a packet buffer, which normally is identified by an index
and resides in the mmapped region.
packet buffers
Fixed size (normally 2 KB) packet buffers allocated by the kernel.
The offset of the struct netmap_if in the mmapped region is indicated by
the nr_offset field in the structure returned by NIOCREGIF. From there,
all other objects are reachable through relative references (offsets or
indexes). Macros and functions in <net/netmap_user.h> help converting
them into actual pointers:
struct netmap_if *nifp = NETMAP_IF(mem, arg.nr_offset);
struct netmap_ring *txr = NETMAP_TXRING(nifp, ring_index);
struct netmap_ring *rxr = NETMAP_RXRING(nifp, ring_index);
char *buf = NETMAP_BUF(ring, buffer_index);
RINGS, BUFFERS AND DATA I/O
Rings are circular queues of packets with three indexes/pointers (head,
cur, tail); one slot is always kept empty. The ring size (num_slots)
should not be assumed to be a power of two.
head is the first slot available to userspace;
cur is the wakeup point: select/poll will unblock when tail passes cur;
tail is the first slot reserved to the kernel.
Slot indexes must only move forward; for convenience, the function
nm_ring_next(ring, index)
returns the next index modulo the ring size.
head and cur are only modified by the user program; tail is only modified
by the kernel. The kernel only reads/writes the struct netmap_ring slots
and buffers during the execution of a netmap-related system call. The
only exception are slots (and buffers) in the range tail ... head-1, that
are explicitly assigned to the kernel.
TRANSMIT RINGS
On transmit rings, after a netmap system call, slots in the range
head ... tail-1 are available for transmission. User code should fill
the slots sequentially and advance head and cur past slots ready to
transmit. cur may be moved further ahead if the user code needs more
slots before further transmissions (see SCATTER GATHER I/O).
At the next NIOCTXSYNC/select()/poll(), slots up to head-1 are pushed to
the port, and tail may advance if further slots have become available.
Below is an example of the evolution of a TX ring:
after the syscall, slots between cur and tail are (a)vailable
head=cur tail
| |
v v
TX [.....aaaaaaaaaaa.............]
user creates new packets to (T)ransmit
head=cur tail
| |
v v
TX [.....TTTTTaaaaaa.............]
NIOCTXSYNC/poll()/select() sends packets and reports new slots
head=cur tail
| |
v v
TX [..........aaaaaaaaaaa........]
select() and poll() will block if there is no space in the ring, i.e.,
ring->cur == ring->tail
and return when new slots have become available.
High speed applications may want to amortize the cost of system calls by
preparing as many packets as possible before issuing them.
A transmit ring with pending transmissions has
ring->head != ring->tail + 1 (modulo the ring size).
The function int nm_tx_pending(ring) implements this test.
RECEIVE RINGS
On receive rings, after a netmap system call, the slots in the range
head... tail-1 contain received packets. User code should process them
and advance head and cur past slots it wants to return to the kernel.
cur may be moved further ahead if the user code wants to wait for more
packets without returning all the previous slots to the kernel.
At the next NIOCRXSYNC/select()/poll(), slots up to head-1 are returned
to the kernel for further receives, and tail may advance to report new
incoming packets.
Below is an example of the evolution of an RX ring:
after the syscall, there are some (h)eld and some (R)eceived slots
head cur tail
| | |
v v v
RX [..hhhhhhRRRRRRRR..........]
user advances head and cur, releasing some slots and holding others
head cur tail
| | |
v v v
RX [..*****hhhRRRRRR...........]
NICRXSYNC/poll()/select() recovers slots and reports new packets
head cur tail
| | |
v v v
RX [.......hhhRRRRRRRRRRRR....]
SLOTS AND PACKET BUFFERS
Normally, packets should be stored in the netmap-allocated buffers
assigned to slots when ports are bound to a file descriptor. One packet
is fully contained in a single buffer.
The following flags affect slot and buffer processing:
NS_BUF_CHANGED
must be used when the buf_idx in the slot is changed. This can be
used to implement zero-copy forwarding, see ZERO-COPY FORWARDING.
NS_REPORT
reports when this buffer has been transmitted. Normally, netmap
notifies transmit completions in batches, hence signals can be
delayed indefinitely. This flag helps detect when packets have been
sent and a file descriptor can be closed.
NS_FORWARD
When a ring is in 'transparent' mode, packets marked with this flag
by the user application are forwarded to the other endpoint at the
next system call, thus restoring (in a selective way) the connection
between a NIC and the host stack.
NS_NO_LEARN
tells the forwarding code that the source MAC address for this
packet must not be used in the learning bridge code.
NS_INDIRECT
indicates that the packet's payload is in a user-supplied buffer
whose user virtual address is in the 'ptr' field of the slot. The
size can reach 65535 bytes.
This is only supported on the transmit ring of VALE ports, and it
helps reducing data copies in the interconnection of virtual
machines.
NS_MOREFRAG
indicates that the packet continues with subsequent buffers; the
last buffer in a packet must have the flag clear.
SCATTER GATHER I/O
Packets can span multiple slots if the NS_MOREFRAG flag is set in all but
the last slot. The maximum length of a chain is 64 buffers. This is
normally used with VALE ports when connecting virtual machines, as they
generate large TSO segments that are not split unless they reach a
physical device.
NOTE: The length field always refers to the individual fragment; there is
no place with the total length of a packet.
On receive rings the macro NS_RFRAGS(slot) indicates the remaining number
of slots for this packet, including the current one. Slots with a value
greater than 1 also have NS_MOREFRAG set.
IOCTLS
netmap uses two ioctls (NIOCTXSYNC, NIOCRXSYNC) for non-blocking I/O.
They take no argument. Two more ioctls (NIOCGINFO, NIOCREGIF) are used
to query and configure ports, with the following argument:
struct nmreq {
char nr_name[IFNAMSIZ]; /* (i) port name */
uint32_t nr_version; /* (i) API version */
uint32_t nr_offset; /* (o) nifp offset in mmap region */
uint32_t nr_memsize; /* (o) size of the mmap region */
uint32_t nr_tx_slots; /* (i/o) slots in tx rings */
uint32_t nr_rx_slots; /* (i/o) slots in rx rings */
uint16_t nr_tx_rings; /* (i/o) number of tx rings */
uint16_t nr_rx_rings; /* (i/o) number of rx rings */
uint16_t nr_ringid; /* (i/o) ring(s) we care about */
uint16_t nr_cmd; /* (i) special command */
uint16_t nr_arg1; /* (i/o) extra arguments */
uint16_t nr_arg2; /* (i/o) extra arguments */
uint32_t nr_arg3; /* (i/o) extra arguments */
uint32_t nr_flags /* (i/o) open mode */
...
};
A file descriptor obtained through /dev/netmap also supports the ioctl
supported by network devices, see netintro(4).
NIOCGINFO
returns EINVAL if the named port does not support netmap.
Otherwise, it returns 0 and (advisory) information about the port.
Note that all the information below can change before the interface
is actually put in netmap mode.
nr_memsize
indicates the size of the netmap memory region. NICs in netmap
mode all share the same memory region, whereas VALE ports have
independent regions for each port.
nr_tx_slots, nr_rx_slots
indicate the size of transmit and receive rings.
nr_tx_rings, nr_rx_rings
indicate the number of transmit and receive rings. Both ring
number and sizes may be configured at runtime using interface-
specific functions (e.g., ethtool(8) ).
NIOCREGIF
binds the port named in nr_name to the file descriptor. For a
physical device this also switches it into netmap mode,
disconnecting it from the host stack. Multiple file descriptors
can be bound to the same port, with proper synchronization left to
the user.
The recommended way to bind a file descriptor to a port is to use
function nm_open(..) (see LIBRARIES) which parses names to access
specific port types and enable features. In the following we
document the main features.
NIOCREGIF can also bind a file descriptor to one endpoint of a
netmap pipe, consisting of two netmap ports with a crossover
connection. A netmap pipe share the same memory space of the
parent port, and is meant to enable configuration where a master
process acts as a dispatcher towards slave processes.
To enable this function, the nr_arg1 field of the structure can be
used as a hint to the kernel to indicate how many pipes we expect
to use, and reserve extra space in the memory region.
On return, it gives the same info as NIOCGINFO, with nr_ringid and
nr_flags indicating the identity of the rings controlled through
the file descriptor.
nr_flags nr_ringid selects which rings are controlled through this
file descriptor. Possible values of nr_flags are indicated below,
together with the naming schemes that application libraries (such
as the nm_open indicated below) can use to indicate the specific
set of rings. In the example below, "netmap:foo" is any valid
netmap port name.
NR_REG_ALL_NIC netmap:foo
(default) all hardware ring pairs
NR_REG_SW netmap:foo^
the ``host rings'', connecting to the host stack.
NR_REG_NIC_SW netmap:foo+
all hardware rings and the host rings
NR_REG_ONE_NIC netmap:foo-i
only the i-th hardware ring pair, where the number is in
nr_ringid;
NR_REG_PIPE_MASTER netmap:foo{i
the master side of the netmap pipe whose identifier (i) is
in nr_ringid;
NR_REG_PIPE_SLAVE netmap:foo}i
the slave side of the netmap pipe whose identifier (i) is in
nr_ringid.
The identifier of a pipe must be thought as part of the pipe
name, and does not need to be sequential. On return the
pipe will only have a single ring pair with index 0,
irrespective of the value of i.
By default, a poll(2) or select(2) call pushes out any pending
packets on the transmit ring, even if no write events are
specified. The feature can be disabled by or-ing NETMAP_NO_TX_POLL
to the value written to nr_ringid. When this feature is used,
packets are transmitted only on ioctl(NIOCTXSYNC) or select() /
poll() are called with a write event (POLLOUT/wfdset) or a full
ring.
When registering a virtual interface that is dynamically created to
a VALE switch, we can specify the desired number of rings (1 by
default, and currently up to 16) on it using nr_tx_rings and
nr_rx_rings fields.
NIOCTXSYNC
tells the hardware of new packets to transmit, and updates the
number of slots available for transmission.
NIOCRXSYNC
tells the hardware of consumed packets, and asks for newly
available packets.
SELECT, POLL, EPOLL, KQUEUE
select(2) and poll(2) on a netmap file descriptor process rings as
indicated in TRANSMIT RINGS and RECEIVE RINGS, respectively when write
(POLLOUT) and read (POLLIN) events are requested. Both block if no slots
are available in the ring (ring->cur == ring->tail). Depending on the
platform, epoll(7) and kqueue(2) are supported too.
Packets in transmit rings are normally pushed out (and buffers reclaimed)
even without requesting write events. Passing the NETMAP_NO_TX_POLL flag
to NIOCREGIF disables this feature. By default, receive rings are
processed only if read events are requested. Passing the
NETMAP_DO_RX_POLL flag to NIOCREGIF updates receive rings even without
read events. Note that on epoll(7) and kqueue(2), NETMAP_NO_TX_POLL and
NETMAP_DO_RX_POLL only have an effect when some event is posted for the
file descriptor.
LIBRARIES
The netmap API is supposed to be used directly, both because of its
simplicity and for efficient integration with applications.
For convenience, the <net/netmap_user.h> header provides a few macros and
functions to ease creating a file descriptor and doing I/O with a netmap
port. These are loosely modeled after the pcap(3) API, to ease porting
of libpcap-based applications to netmap. To use these extra functions,
programs should
#define NETMAP_WITH_LIBS
before
#include <net/netmap_user.h>
The following functions are available:
struct nm_desc * nm_open(const char *ifname, const struct nmreq *req,
uint64_t flags, const struct nm_desc *arg)
similar to pcap_open_live(3), binds a file descriptor to a port.
ifname
is a port name, in the form "netmap:PPP" for a NIC and
"valeSSS:PPP" for a VALE port.
req
provides the initial values for the argument to the NIOCREGIF
ioctl. The nm_flags and nm_ringid values are overwritten by
parsing ifname and flags, and other fields can be overridden
through the other two arguments.
arg
points to a struct nm_desc containing arguments (e.g., from a
previously open file descriptor) that should override the
defaults. The fields are used as described below
flags
can be set to a combination of the following flags:
NETMAP_NO_TX_POLL, NETMAP_DO_RX_POLL (copied into nr_ringid);
NM_OPEN_NO_MMAP (if arg points to the same memory region,
avoids the mmap and uses the values from it); NM_OPEN_IFNAME
(ignores ifname and uses the values in arg); NM_OPEN_ARG1,
NM_OPEN_ARG2, NM_OPEN_ARG3 (uses the fields from arg);
NM_OPEN_RING_CFG (uses the ring number and sizes from arg).
int nm_close(struct nm_desc *d)
closes the file descriptor, unmaps memory, frees resources.
int nm_inject(struct nm_desc *d, const void *buf, size_t size)
similar to pcap_inject(), pushes a packet to a ring, returns the
size of the packet is successful, or 0 on error;
int nm_dispatch(struct nm_desc *d, int cnt, nm_cb_t cb, u_char *arg)
similar to pcap_dispatch(), applies a callback to incoming packets
u_char * nm_nextpkt(struct nm_desc *d, struct nm_pkthdr *hdr)
similar to pcap_next(), fetches the next packet
SUPPORTED DEVICES
netmap natively supports the following devices:
On FreeBSD: cxgbe(4), em(4), iflib(4) (providing igb(4) and em(4)),
ixgbe(4), ixl(4), re(4), vtnet(4).
On Linux e1000, e1000e, i40e, igb, ixgbe, ixgbevf, r8169, virtio_net,
vmxnet3.
NICs without native support can still be used in netmap mode through
emulation. Performance is inferior to native netmap mode but still
significantly higher than various raw socket types (bpf, PF_PACKET,
etc.). Note that for slow devices (such as 1 Gbit/s and slower NICs, or
several 10 Gbit/s NICs whose hardware is unable to sustain line rate),
emulated and native mode will likely have similar or same throughput.
When emulation is in use, packet sniffer programs such as tcpdump could
see received packets before they are diverted by netmap. This behaviour
is not intentional, being just an artifact of the implementation of
emulation. Note that in case the netmap application subsequently moves
packets received from the emulated adapter onto the host RX ring, the
sniffer will intercept those packets again, since the packets are
injected to the host stack as they were received by the network
interface.
Emulation is also available for devices with native netmap support, which
can be used for testing or performance comparison. The sysctl variable
dev.netmap.admode globally controls how netmap mode is implemented.
SYSCTL VARIABLES AND MODULE PARAMETERS
Some aspects of the operation of netmap and VALE are controlled through
sysctl variables on FreeBSD (dev.netmap.*) and module parameters on Linux
(/sys/module/netmap/parameters/*):
dev.netmap.admode: 0
Controls the use of native or emulated adapter mode.
0 uses the best available option;
1 forces native mode and fails if not available;
2 forces emulated hence never fails.
dev.netmap.generic_rings: 1
Number of rings used for emulated netmap mode
dev.netmap.generic_ringsize: 1024
Ring size used for emulated netmap mode
dev.netmap.generic_mit: 100000
Controls interrupt moderation for emulated mode
dev.netmap.fwd: 0
Forces NS_FORWARD mode
dev.netmap.txsync_retry: 2
Number of txsync loops in the VALE flush function
dev.netmap.no_pendintr: 1
Forces recovery of transmit buffers on system calls
dev.netmap.no_timestamp: 0
Disables the update of the timestamp in the netmap ring
dev.netmap.verbose: 0
Verbose kernel messages
dev.netmap.buf_num: 163840
dev.netmap.buf_size: 2048
dev.netmap.ring_num: 200
dev.netmap.ring_size: 36864
dev.netmap.if_num: 100
dev.netmap.if_size: 1024
Sizes and number of objects (netmap_if, netmap_ring, buffers) for
the global memory region. The only parameter worth modifying is
dev.netmap.buf_num as it impacts the total amount of memory used
by netmap.
dev.netmap.buf_curr_num: 0
dev.netmap.buf_curr_size: 0
dev.netmap.ring_curr_num: 0
dev.netmap.ring_curr_size: 0
dev.netmap.if_curr_num: 0
dev.netmap.if_curr_size: 0
Actual values in use.
dev.netmap.priv_buf_num: 4098
dev.netmap.priv_buf_size: 2048
dev.netmap.priv_ring_num: 4
dev.netmap.priv_ring_size: 20480
dev.netmap.priv_if_num: 2
dev.netmap.priv_if_size: 1024
Sizes and number of objects (netmap_if, netmap_ring, buffers) for
private memory regions. A separate memory region is used for
each VALE port and each pair of netmap pipes.
dev.netmap.bridge_batch: 1024
Batch size used when moving packets across a VALE switch. Values
above 64 generally guarantee good performance.
dev.netmap.ptnet_vnet_hdr: 1
Allow ptnet devices to use virtio-net headers
SYSTEM CALLS
netmap uses select(2), poll(2), epoll(7) and kqueue(2) to wake up
processes when significant events occur, and mmap(2) to map memory.
ioctl(2) is used to configure ports and VALE switches.
Applications may need to create threads and bind them to specific cores
to improve performance, using standard OS primitives, see pthread(3). In
particular, pthread_setaffinity_np(3) may be of use.
EXAMPLES
TEST PROGRAMS
netmap comes with a few programs that can be used for testing or simple
applications. See the examples/ directory in netmap distributions, or
tools/tools/netmap/ directory in FreeBSD distributions.
pkt-gen(8) is a general purpose traffic source/sink.
As an example
pkt-gen -i ix0 -f tx -l 60
can generate an infinite stream of minimum size packets, and
pkt-gen -i ix0 -f rx
is a traffic sink. Both print traffic statistics, to help monitor how
the system performs.
pkt-gen(8) has many options can be uses to set packet sizes, addresses,
rates, and use multiple send/receive threads and cores.
bridge(4) is another test program which interconnects two netmap ports.
It can be used for transparent forwarding between interfaces, as in
bridge -i netmap:ix0 -i netmap:ix1
or even connect the NIC to the host stack using netmap
bridge -i netmap:ix0
USING THE NATIVE API
The following code implements a traffic generator:
#include <net/netmap_user.h>
...
void sender(void)
{
struct netmap_if *nifp;
struct netmap_ring *ring;
struct nmreq nmr;
struct pollfd fds;
fd = open("/dev/netmap", O_RDWR);
bzero(&nmr, sizeof(nmr));
strcpy(nmr.nr_name, "ix0");
nmr.nm_version = NETMAP_API;
ioctl(fd, NIOCREGIF, &nmr);
p = mmap(0, nmr.nr_memsize, fd);
nifp = NETMAP_IF(p, nmr.nr_offset);
ring = NETMAP_TXRING(nifp, 0);
fds.fd = fd;
fds.events = POLLOUT;
for (;;) {
poll(&fds, 1, -1);
while (!nm_ring_empty(ring)) {
i = ring->cur;
buf = NETMAP_BUF(ring, ring->slot[i].buf_index);
... prepare packet in buf ...
ring->slot[i].len = ... packet length ...
ring->head = ring->cur = nm_ring_next(ring, i);
}
}
}
HELPER FUNCTIONS
A simple receiver can be implemented using the helper functions:
#define NETMAP_WITH_LIBS
#include <net/netmap_user.h>
...
void receiver(void)
{
struct nm_desc *d;
struct pollfd fds;
u_char *buf;
struct nm_pkthdr h;
...
d = nm_open("netmap:ix0", NULL, 0, 0);
fds.fd = NETMAP_FD(d);
fds.events = POLLIN;
for (;;) {
poll(&fds, 1, -1);
while ( (buf = nm_nextpkt(d, &h)) )
consume_pkt(buf, h.len);
}
nm_close(d);
}
ZERO-COPY FORWARDING
Since physical interfaces share the same memory region, it is possible to
do packet forwarding between ports swapping buffers. The buffer from the
transmit ring is used to replenish the receive ring:
uint32_t tmp;
struct netmap_slot *src, *dst;
...
src = &src_ring->slot[rxr->cur];
dst = &dst_ring->slot[txr->cur];
tmp = dst->buf_idx;
dst->buf_idx = src->buf_idx;
dst->len = src->len;
dst->flags = NS_BUF_CHANGED;
src->buf_idx = tmp;
src->flags = NS_BUF_CHANGED;
rxr->head = rxr->cur = nm_ring_next(rxr, rxr->cur);
txr->head = txr->cur = nm_ring_next(txr, txr->cur);
...
ACCESSING THE HOST STACK
The host stack is for all practical purposes just a regular ring pair,
which you can access with the netmap API (e.g., with
nm_open("netmap:eth0^", ...);
All packets that the host would send to an interface in netmap mode end
up into the RX ring, whereas all packets queued to the TX ring are send
up to the host stack.
VALE SWITCH
A simple way to test the performance of a VALE switch is to attach a
sender and a receiver to it, e.g., running the following in two different
terminals:
pkt-gen -i vale1:a -f rx # receiver
pkt-gen -i vale1:b -f tx # sender
The same example can be used to test netmap pipes, by simply changing
port names, e.g.,
pkt-gen -i vale2:x{3 -f rx # receiver on the master side
pkt-gen -i vale2:x}3 -f tx # sender on the slave side
The following command attaches an interface and the host stack to a
switch:
valectl -h vale2:em0
Other netmap clients attached to the same switch can now communicate with
the network card or the host.
SEE ALSO
vale(4), valectl(8), bridge(8), lb(8), nmreplay(8), pkt-gen(8)
http://info.iet.unipi.it/~luigi/netmap/
Luigi Rizzo, Revisiting network I/O APIs: the netmap framework,
Communications of the ACM, 55 (3), pp.45-51, March 2012
Luigi Rizzo, netmap: a novel framework for fast packet I/O, Usenix
ATC'12, June 2012, Boston
Luigi Rizzo, Giuseppe Lettieri, VALE, a switched ethernet for virtual
machines, ACM CoNEXT'12, December 2012, Nice
Luigi Rizzo, Giuseppe Lettieri, Vincenzo Maffione, Speeding up packet I/O
in virtual machines, ACM/IEEE ANCS'13, October 2013, San Jose
AUTHORS
The netmap framework has been originally designed and implemented at the
Universita` di Pisa in 2011 by Luigi Rizzo, and further extended with
help from Matteo Landi, Gaetano Catalli, Giuseppe Lettieri, and Vincenzo
Maffione.
netmap and VALE have been funded by the European Commission within FP7
Projects CHANGE (257422) and OPENLAB (287581).
CAVEATS
No matter how fast the CPU and OS are, achieving line rate on 10G and
faster interfaces requires hardware with sufficient performance. Several
NICs are unable to sustain line rate with small packet sizes.
Insufficient PCIe or memory bandwidth can also cause reduced performance.
Another frequent reason for low performance is the use of flow control on
the link: a slow receiver can limit the transmit speed. Be sure to
disable flow control when running high speed experiments.
SPECIAL NIC FEATURES
netmap is orthogonal to some NIC features such as multiqueue, schedulers,
packet filters.
Multiple transmit and receive rings are supported natively and can be
configured with ordinary OS tools, such as ethtool(8) or device-specific
sysctl variables. The same goes for Receive Packet Steering (RPS) and
filtering of incoming traffic.
netmap does not use features such as checksum offloading, TCP
segmentation offloading, encryption, VLAN encapsulation/decapsulation,
etc. When using netmap to exchange packets with the host stack, make
sure to disable these features.
FreeBSD 13.1-RELEASE-p6 October 3, 2020 FreeBSD 13.1-RELEASE-p6
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