Lines Matching +full:two +full:- +full:user
1 .. SPDX-License-Identifier: GPL-2.0
20 XDP programs to redirect frames to a memory buffer in a user-space
24 syscall. Associated with each XSK are two rings: the RX ring and the
38 is simply an offset within the entire UMEM region. The user space
42 UMEM also has two rings: the FILL ring and the COMPLETION ring. The
47 kernel has transmitted completely and can now be used again by user
59 corresponding two rings, sets the XDP_SHARED_UMEM flag in the bind
64 single-consumer / single-producer (for performance reasons), the new
72 user-space application can place an XSK at an arbitrary place in this
79 traffic to user space through the XSK.
81 AF_XDP can operate in two different modes: XDP_SKB and XDP_DRV. If the
84 together with the generic XDP support and copies out the data to user
88 data into user space.
99 http://vger.kernel.org/lpc_net2018_talks/lpc18_paper_af_xdp_perf-v2.pdf. Do
106 ----
109 equal-sized frames. An UMEM is associated to a netdev and a specific
121 The UMEM has two single-producer/single-consumer rings that are used
123 user-space application.
126 -----
129 TX. All rings are single-producer/single-consumer, so the user-space
133 The UMEM uses two rings: FILL and COMPLETION. Each socket associated
145 calls and mmapped to user-space using the appropriate offset to mmap()
149 The size of the rings need to be of size power of two.
155 user-space to kernel-space. The UMEM addrs are passed in the ring. As
161 The user application produces UMEM addrs to this ring. Note that, if
165 to the same chunk. If the user application is run in the unaligned
173 kernel-space to user-space. Just like the FILL ring, UMEM indices are
176 Frames passed from the kernel to user-space are frames that has been
177 sent (TX ring) and can be used by user-space again.
179 The user application consumes UMEM addrs from this ring.
192 The user application consumes struct xdp_desc descriptors from this
204 The user application produces struct xdp_desc descriptors to this
213 AF_XDP. It contains two types of functions: those that can be used to
218 user. It will make your program a lot simpler.
227 The user application inserts the socket into the map, via the bpf()
244 ------------------------------------
246 When you bind to a socket, the kernel will first try to use zero-copy
247 copy. If zero-copy is not supported, it will fall back on using copy
248 mode, i.e. copying all packets out to user space. But if you would
253 socket into zero-copy mode or fail.
256 -------------------------
280 round-robin example of distributing packets is shown below:
282 .. code-block:: c
300 rr = (rr + 1) & (MAX_SOCKS - 1);
320 netdev,queue_id pair. Let us say you want to create two sockets bound
321 to two different queue ids on the same netdev. Create the first socket
327 socket. These two sockets will now share one and the same UMEM.
348 -----------------------------
351 present in the FILL ring and the TX ring, the rings for which user
363 need_wakeup flag is set so that user space can put buffers on the
375 .. code-block:: c
389 ------------------------------------------------------
401 be used. Note, that the rings are single-producer single-consumer, so
405 In libbpf, you can create Rx-only and Tx-only sockets by supplying
409 If you create a Tx-only socket, we recommend that you do not put any
415 -----------------------
433 --------------------------
437 is created by a privileged process and passed to a non-privileged one.
442 --------------------------------
446 mode to allow application to tune the per-socket maximum iteration for
448 Allowed range is [32, xs->tx->nentries].
451 -------------------------
456 .. code-block:: c
465 ----------------------
468 XDP_OPTIONS_ZEROCOPY which tells you if zero-copy is on or not.
470 Multi-Buffer Support
473 With multi-buffer support, programs using AF_XDP sockets can receive
475 zero-copy mode. For example, a packet can consist of two
488 To enable multi-buffer support for an AF_XDP socket, use the new bind
489 flag XDP_USE_SG. If this is not provided, all multi-buffer packets
491 needs to be in multi-buffer mode. This can be accomplished by using
498 of the packet. Why the reverse logic of end-of-packet (eop) flag found
499 in many NICs? Just to preserve compatibility with non-multi-buffer
523 * For zero-copy mode, the limit is up to what the NIC HW
526 CONFIG_MAX_SKB_FRAGS + 1) for zero-copy mode, as it would have
528 NIC supports. Kind of defeats the purpose of zero-copy mode. How to
529 probe for this limit is explained in the "probe for multi-buffer
532 On the Rx path in copy-mode, the xsk core copies the XDP data into
534 detailed before. Zero-copy mode works the same, though the data is not
551 An example program each for Rx and Tx multi-buffer support can be found
555 -----
557 In order to use AF_XDP sockets two parts are needed. The user-space
559 please refer to the xdp-project at
560 https://github.com/xdp-project/bpf-examples/tree/main/AF_XDP-example.
564 .. code-block:: c
568 int index = ctx->rx_queue_index;
581 .. code-block:: c
603 __u32 entries = *ring->producer - *ring->consumer;
606 return -1;
608 // read-barrier!
610 *item = ring->desc[*ring->consumer & (RING_SIZE - 1)];
611 (*ring->consumer)++;
617 u32 free_entries = RING_SIZE - (*ring->producer - *ring->consumer);
620 return -1;
622 ring->desc[*ring->producer & (RING_SIZE - 1)] = *item;
624 // write-barrier!
626 (*ring->producer)++;
633 Usage Multi-Buffer Rx
634 ---------------------
636 Here is a simple Rx path pseudo-code example (using libxdp interfaces
639 .. code-block:: c
647 int rcvd = xsk_ring_cons__peek(&xsk->rx, opt_batch_size, &idx_rx);
649 xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
652 struct xdp_desc *desc = xsk_ring_cons__rx_desc(&xsk->rx, idx_rx++);
653 char *frag = xsk_umem__get_data(xsk->umem->buffer, desc->addr);
654 bool eop = !(desc->options & XDP_PKT_CONTD);
666 *xsk_ring_prod__fill_addr(&xsk->umem->fq, idx_fq++) = desc->addr;
669 xsk_ring_prod__submit(&xsk->umem->fq, rcvd);
670 xsk_ring_cons__release(&xsk->rx, rcvd);
673 Usage Multi-Buffer Tx
674 ---------------------
676 Here is an example Tx path pseudo-code (using libxdp interfaces for
681 .. code-block:: c
688 xsk_ring_prod__reserve(&xsk->tx, batch_size, &idx);
697 tx_desc = xsk_ring_prod__tx_desc(&xsk->tx, idx + i++);
698 tx_desc->addr = addr;
701 tx_desc->len = xsk_frame_size;
702 tx_desc->options = XDP_PKT_CONTD;
704 tx_desc->len = len;
705 tx_desc->options = 0;
708 len -= tx_desc->len;
720 xsk_ring_prod__submit(&xsk->tx, i);
723 Probing for Multi-Buffer Support
724 --------------------------------
726 To discover if a driver supports multi-buffer AF_XDP in SKB or DRV
729 querying for XDP multi-buffer support. If XDP supports multi-buffer in
732 To discover if a driver supports multi-buffer AF_XDP in zero-copy
734 flag. If it is set, it means that at least zero-copy is supported and
738 supported by this device in zero-copy mode. These are the possible
741 1: Multi-buffer for zero-copy is not supported by this device, as max
742 one fragment supported means that multi-buffer is not possible.
744 >=2: Multi-buffer is supported in zero-copy mode for this device. The
750 Multi-Buffer Support for Zero-Copy Drivers
751 ------------------------------------------
753 Zero-copy drivers usually use the batched APIs for Rx and Tx
756 to facilitate extending a zero-copy driver with multi-buffer support.
761 https://github.com/xdp-project/bpf-examples/tree/main/AF_XDP-example
767 ethtool -N p3p2 rx-flow-hash udp4 fn
768 ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
774 samples/bpf/xdpsock -i p3p2 -q 16 -r -N
776 For XDP_SKB mode, use the switch "-S" instead of "-N" and all options
777 can be displayed with "-h", as usual.
805 sudo ethtool -L <interface> combined 1
812 sudo ethtool -N <interface> rx-flow-hash udp4 fn
813 sudo ethtool -N <interface> flow-type udp4 src-port 4242 dst-port \
827 to the same queue id Y. In zero-copy mode, you should use the
845 - Björn Töpel (AF_XDP core)
846 - Magnus Karlsson (AF_XDP core)
847 - Alexander Duyck
848 - Alexei Starovoitov
849 - Daniel Borkmann
850 - Jesper Dangaard Brouer
851 - John Fastabend
852 - Jonathan Corbet (LWN coverage)
853 - Michael S. Tsirkin
854 - Qi Z Zhang
855 - Willem de Bruijn