Lines Matching +full:mode +full:- +full:flag
1 .. SPDX-License-Identifier: GPL-2.0
20 XDP programs to redirect frames to a memory buffer in a user-space
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
83 when loading the XDP program, XDP_SKB mode is employed that uses SKBs
85 space. A fallback mode that works for any network device. On the other
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
117 the next socket B can do this by setting the XDP_SHARED_UMEM flag in
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
145 calls and mmapped to user-space using the appropriate offset to mmap()
155 user-space to kernel-space. The UMEM addrs are passed in the ring. As
162 running the application with aligned chunk mode, the kernel will mask
166 chunks mode, then the incoming addr will be left untouched.
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.
247 ------------------------------------
249 When you bind to a socket, the kernel will first try to use zero-copy
250 copy. If zero-copy is not supported, it will fall back on using copy
251 mode, i.e. copying all packets out to user space. But if you would
252 like to force a certain mode, you can use the following flags. If you
253 pass the XDP_COPY flag to the bind call, the kernel will force the
254 socket into copy mode. If it cannot use copy mode, the bind call will
255 fail with an error. Conversely, the XDP_ZEROCOPY flag will force the
256 socket into zero-copy mode or fail.
258 XDP_SHARED_UMEM bind flag
259 -------------------------
261 This flag enables you to bind multiple sockets to the same UMEM. It
263 netdevs/devices. In this mode, each socket has their own RX and TX
272 we have bound to. To use this mode, create the first socket and bind
283 round-robin example of distributing packets is shown below:
285 .. code-block:: c
303 rr = (rr + 1) & (MAX_SOCKS - 1);
314 Libbpf uses this mode if you create more than one socket tied to the
350 XDP_USE_NEED_WAKEUP bind flag
351 -----------------------------
353 This option adds support for a new flag called need_wakeup that is
356 need_wakeup flag will be set if the kernel needs to be explicitly
357 woken up by a syscall to continue processing packets. If the flag is
360 If the flag is set on the FILL ring, the application needs to call
366 need_wakeup flag is set so that user space can put buffers on the
370 If the flag is set for the TX ring, it means that the application
375 An example of how to use this flag can be found in
379 .. code-block:: c
384 I.e., only use the syscall if the flag is set.
386 We recommend that you always enable this mode as it usually leads to
393 ------------------------------------------------------
402 socket. But if the XDP_SHARED_UMEM flag is used, any socket after the
405 be used. Note, that the rings are single-producer single-consumer, so
409 In libbpf, you can create Rx-only and Tx-only sockets by supplying
413 If you create a Tx-only socket, we recommend that you do not put any
419 -----------------------
434 be dealt with in separate sections for each UMEM flag.
437 --------------------------
441 is created by a privileged process and passed to a non-privileged one.
446 -------------------------
451 .. code-block:: c
460 ----------------------
463 XDP_OPTIONS_ZEROCOPY which tells you if zero-copy is on or not.
465 Multi-Buffer Support
468 With multi-buffer support, programs using AF_XDP sockets can receive
470 zero-copy mode. For example, a packet can consist of two
483 To enable multi-buffer support for an AF_XDP socket, use the new bind
484 flag XDP_USE_SG. If this is not provided, all multi-buffer packets
486 needs to be in multi-buffer mode. This can be accomplished by using
489 To represent a packet consisting of multiple frames, a new flag called
493 of the packet. Why the reverse logic of end-of-packet (eop) flag found
494 in many NICs? Just to preserve compatibility with non-multi-buffer
511 * For copy mode, the maximum supported number of frames in a packet is
518 * For zero-copy mode, the limit is up to what the NIC HW
521 CONFIG_MAX_SKB_FRAGS + 1) for zero-copy mode, as it would have
523 NIC supports. Kind of defeats the purpose of zero-copy mode. How to
524 probe for this limit is explained in the "probe for multi-buffer
527 On the Rx path in copy-mode, the xsk core copies the XDP data into
528 multiple descriptors, if needed, and sets the XDP_PKT_CONTD flag as
529 detailed before. Zero-copy mode works the same, though the data is not
531 flag set to one, it means that the packet consists of multiple buffers
546 An example program each for Rx and Tx multi-buffer support can be found
550 -----
553 user-space application and the XDP program. For a complete setup and
554 usage example, please refer to the sample application. The user-space
559 .. code-block:: c
563 int index = ctx->rx_queue_index;
576 .. code-block:: c
598 __u32 entries = *ring->producer - *ring->consumer;
601 return -1;
603 // read-barrier!
605 *item = ring->desc[*ring->consumer & (RING_SIZE - 1)];
606 (*ring->consumer)++;
612 u32 free_entries = RING_SIZE - (*ring->producer - *ring->consumer);
615 return -1;
617 ring->desc[*ring->producer & (RING_SIZE - 1)] = *item;
619 // write-barrier!
621 (*ring->producer)++;
628 Usage Multi-Buffer Rx
629 ---------------------
631 Here is a simple Rx path pseudo-code example (using libxdp interfaces
634 .. code-block:: c
642 int rcvd = xsk_ring_cons__peek(&xsk->rx, opt_batch_size, &idx_rx);
644 xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
647 struct xdp_desc *desc = xsk_ring_cons__rx_desc(&xsk->rx, idx_rx++);
648 char *frag = xsk_umem__get_data(xsk->umem->buffer, desc->addr);
649 bool eop = !(desc->options & XDP_PKT_CONTD);
661 *xsk_ring_prod__fill_addr(&xsk->umem->fq, idx_fq++) = desc->addr;
664 xsk_ring_prod__submit(&xsk->umem->fq, rcvd);
665 xsk_ring_cons__release(&xsk->rx, rcvd);
668 Usage Multi-Buffer Tx
669 ---------------------
671 Here is an example Tx path pseudo-code (using libxdp interfaces for
676 .. code-block:: c
683 xsk_ring_prod__reserve(&xsk->tx, batch_size, &idx);
692 tx_desc = xsk_ring_prod__tx_desc(&xsk->tx, idx + i++);
693 tx_desc->addr = addr;
696 tx_desc->len = xsk_frame_size;
697 tx_desc->options = XDP_PKT_CONTD;
699 tx_desc->len = len;
700 tx_desc->options = 0;
703 len -= tx_desc->len;
715 xsk_ring_prod__submit(&xsk->tx, i);
718 Probing for Multi-Buffer Support
719 --------------------------------
721 To discover if a driver supports multi-buffer AF_XDP in SKB or DRV
722 mode, use the XDP_FEATURES feature of netlink in linux/netdev.h to
723 query for NETDEV_XDP_ACT_RX_SG support. This is the same flag as for
724 querying for XDP multi-buffer support. If XDP supports multi-buffer in
725 a driver, then AF_XDP will also support that in SKB and DRV mode.
727 To discover if a driver supports multi-buffer AF_XDP in zero-copy
728 mode, use XDP_FEATURES and first check the NETDEV_XDP_ACT_XSK_ZEROCOPY
729 flag. If it is set, it means that at least zero-copy is supported and
733 supported by this device in zero-copy mode. These are the possible
736 1: Multi-buffer for zero-copy is not supported by this device, as max
737 one fragment supported means that multi-buffer is not possible.
739 >=2: Multi-buffer is supported in zero-copy mode for this device. The
745 Multi-Buffer Support for Zero-Copy Drivers
746 ------------------------------------------
748 Zero-copy drivers usually use the batched APIs for Rx and Tx
751 to facilitate extending a zero-copy driver with multi-buffer support.
761 ethtool -N p3p2 rx-flow-hash udp4 fn
762 ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
765 Running the rxdrop benchmark in XDP_DRV mode can then be done
768 samples/bpf/xdpsock -i p3p2 -q 16 -r -N
770 For XDP_SKB mode, use the switch "-S" instead of "-N" and all options
771 can be displayed with "-h", as usual.
799 sudo ethtool -L <interface> combined 1
806 sudo ethtool -N <interface> rx-flow-hash udp4 fn
807 sudo ethtool -N <interface> flow-type udp4 src-port 4242 dst-port \
814 in copy mode?
821 to the same queue id Y. In zero-copy mode, you should use the
834 XDP_SHARED_UMEM flag.
839 - Björn Töpel (AF_XDP core)
840 - Magnus Karlsson (AF_XDP core)
841 - Alexander Duyck
842 - Alexei Starovoitov
843 - Daniel Borkmann
844 - Jesper Dangaard Brouer
845 - John Fastabend
846 - Jonathan Corbet (LWN coverage)
847 - Michael S. Tsirkin
848 - Qi Z Zhang
849 - Willem de Bruijn