diff options
Diffstat (limited to 'Documentation/networking')
| -rw-r--r-- | Documentation/networking/af_xdp.rst | 297 | ||||
| -rw-r--r-- | Documentation/networking/bonding.txt | 2 | ||||
| -rw-r--r-- | Documentation/networking/filter.txt | 21 | ||||
| -rw-r--r-- | Documentation/networking/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/networking/ip-sysctl.txt | 30 | ||||
| -rw-r--r-- | Documentation/networking/netdev-features.txt | 7 |
6 files changed, 350 insertions, 8 deletions
diff --git a/Documentation/networking/af_xdp.rst b/Documentation/networking/af_xdp.rst new file mode 100644 index 000000000000..91928d9ee4bf --- /dev/null +++ b/Documentation/networking/af_xdp.rst @@ -0,0 +1,297 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====== +AF_XDP +====== + +Overview +======== + +AF_XDP is an address family that is optimized for high performance +packet processing. + +This document assumes that the reader is familiar with BPF and XDP. If +not, the Cilium project has an excellent reference guide at +http://cilium.readthedocs.io/en/doc-1.0/bpf/. + +Using the XDP_REDIRECT action from an XDP program, the program can +redirect ingress frames to other XDP enabled netdevs, using the +bpf_redirect_map() function. AF_XDP sockets enable the possibility for +XDP programs to redirect frames to a memory buffer in a user-space +application. + +An AF_XDP socket (XSK) is created with the normal socket() +syscall. Associated with each XSK are two rings: the RX ring and the +TX ring. A socket can receive packets on the RX ring and it can send +packets on the TX ring. These rings are registered and sized with the +setsockopts XDP_RX_RING and XDP_TX_RING, respectively. It is mandatory +to have at least one of these rings for each socket. An RX or TX +descriptor ring points to a data buffer in a memory area called a +UMEM. RX and TX can share the same UMEM so that a packet does not have +to be copied between RX and TX. Moreover, if a packet needs to be kept +for a while due to a possible retransmit, the descriptor that points +to that packet can be changed to point to another and reused right +away. This again avoids copying data. + +The UMEM consists of a number of equally size frames and each frame +has a unique frame id. A descriptor in one of the rings references a +frame by referencing its frame id. The user space allocates memory for +this UMEM using whatever means it feels is most appropriate (malloc, +mmap, huge pages, etc). This memory area is then registered with the +kernel using the new setsockopt XDP_UMEM_REG. The UMEM also has two +rings: the FILL ring and the COMPLETION ring. The fill ring is used by +the application to send down frame ids for the kernel to fill in with +RX packet data. References to these frames will then appear in the RX +ring once each packet has been received. The completion ring, on the +other hand, contains frame ids that the kernel has transmitted +completely and can now be used again by user space, for either TX or +RX. Thus, the frame ids appearing in the completion ring are ids that +were previously transmitted using the TX ring. In summary, the RX and +FILL rings are used for the RX path and the TX and COMPLETION rings +are used for the TX path. + +The socket is then finally bound with a bind() call to a device and a +specific queue id on that device, and it is not until bind is +completed that traffic starts to flow. + +The UMEM can be shared between processes, if desired. If a process +wants to do this, it simply skips the registration of the UMEM and its +corresponding two rings, sets the XDP_SHARED_UMEM flag in the bind +call and submits the XSK of the process it would like to share UMEM +with as well as its own newly created XSK socket. The new process will +then receive frame id references in its own RX ring that point to this +shared UMEM. Note that since the ring structures are single-consumer / +single-producer (for performance reasons), the new process has to +create its own socket with associated RX and TX rings, since it cannot +share this with the other process. This is also the reason that there +is only one set of FILL and COMPLETION rings per UMEM. It is the +responsibility of a single process to handle the UMEM. + +How is then packets distributed from an XDP program to the XSKs? There +is a BPF map called XSKMAP (or BPF_MAP_TYPE_XSKMAP in full). The +user-space application can place an XSK at an arbitrary place in this +map. The XDP program can then redirect a packet to a specific index in +this map and at this point XDP validates that the XSK in that map was +indeed bound to that device and ring number. If not, the packet is +dropped. If the map is empty at that index, the packet is also +dropped. This also means that it is currently mandatory to have an XDP +program loaded (and one XSK in the XSKMAP) to be able to get any +traffic to user space through the XSK. + +AF_XDP can operate in two different modes: XDP_SKB and XDP_DRV. If the +driver does not have support for XDP, or XDP_SKB is explicitly chosen +when loading the XDP program, XDP_SKB mode is employed that uses SKBs +together with the generic XDP support and copies out the data to user +space. A fallback mode that works for any network device. On the other +hand, if the driver has support for XDP, it will be used by the AF_XDP +code to provide better performance, but there is still a copy of the +data into user space. + +Concepts +======== + +In order to use an AF_XDP socket, a number of associated objects need +to be setup. + +Jonathan Corbet has also written an excellent article on LWN, +"Accelerating networking with AF_XDP". It can be found at +https://lwn.net/Articles/750845/. + +UMEM +---- + +UMEM is a region of virtual contiguous memory, divided into +equal-sized frames. An UMEM is associated to a netdev and a specific +queue id of that netdev. It is created and configured (frame size, +frame headroom, start address and size) by using the XDP_UMEM_REG +setsockopt system call. A UMEM is bound to a netdev and queue id, via +the bind() system call. + +An AF_XDP is socket linked to a single UMEM, but one UMEM can have +multiple AF_XDP sockets. To share an UMEM created via one socket A, +the next socket B can do this by setting the XDP_SHARED_UMEM flag in +struct sockaddr_xdp member sxdp_flags, and passing the file descriptor +of A to struct sockaddr_xdp member sxdp_shared_umem_fd. + +The UMEM has two single-producer/single-consumer rings, that are used +to transfer ownership of UMEM frames between the kernel and the +user-space application. + +Rings +----- + +There are a four different kind of rings: Fill, Completion, RX and +TX. All rings are single-producer/single-consumer, so the user-space +application need explicit synchronization of multiple +processes/threads are reading/writing to them. + +The UMEM uses two rings: Fill and Completion. Each socket associated +with the UMEM must have an RX queue, TX queue or both. Say, that there +is a setup with four sockets (all doing TX and RX). Then there will be +one Fill ring, one Completion ring, four TX rings and four RX rings. + +The rings are head(producer)/tail(consumer) based rings. A producer +writes the data ring at the index pointed out by struct xdp_ring +producer member, and increasing the producer index. A consumer reads +the data ring at the index pointed out by struct xdp_ring consumer +member, and increasing the consumer index. + +The rings are configured and created via the _RING setsockopt system +calls and mmapped to user-space using the appropriate offset to mmap() +(XDP_PGOFF_RX_RING, XDP_PGOFF_TX_RING, XDP_UMEM_PGOFF_FILL_RING and +XDP_UMEM_PGOFF_COMPLETION_RING). + +The size of the rings need to be of size power of two. + +UMEM Fill Ring +~~~~~~~~~~~~~~ + +The Fill ring is used to transfer ownership of UMEM frames from +user-space to kernel-space. The UMEM indicies are passed in the +ring. As an example, if the UMEM is 64k and each frame is 4k, then the +UMEM has 16 frames and can pass indicies between 0 and 15. + +Frames passed to the kernel are used for the ingress path (RX rings). + +The user application produces UMEM indicies to this ring. + +UMEM Completetion Ring +~~~~~~~~~~~~~~~~~~~~~~ + +The Completion Ring is used transfer ownership of UMEM frames from +kernel-space to user-space. Just like the Fill ring, UMEM indicies are +used. + +Frames passed from the kernel to user-space are frames that has been +sent (TX ring) and can be used by user-space again. + +The user application consumes UMEM indicies from this ring. + + +RX Ring +~~~~~~~ + +The RX ring is the receiving side of a socket. Each entry in the ring +is a struct xdp_desc descriptor. The descriptor contains UMEM index +(idx), the length of the data (len), the offset into the frame +(offset). + +If no frames have been passed to kernel via the Fill ring, no +descriptors will (or can) appear on the RX ring. + +The user application consumes struct xdp_desc descriptors from this +ring. + +TX Ring +~~~~~~~ + +The TX ring is used to send frames. The struct xdp_desc descriptor is +filled (index, length and offset) and passed into the ring. + +To start the transfer a sendmsg() system call is required. This might +be relaxed in the future. + +The user application produces struct xdp_desc descriptors to this +ring. + +XSKMAP / BPF_MAP_TYPE_XSKMAP +---------------------------- + +On XDP side there is a BPF map type BPF_MAP_TYPE_XSKMAP (XSKMAP) that +is used in conjunction with bpf_redirect_map() to pass the ingress +frame to a socket. + +The user application inserts the socket into the map, via the bpf() +system call. + +Note that if an XDP program tries to redirect to a socket that does +not match the queue configuration and netdev, the frame will be +dropped. E.g. an AF_XDP socket is bound to netdev eth0 and +queue 17. Only the XDP program executing for eth0 and queue 17 will +successfully pass data to the socket. Please refer to the sample +application (samples/bpf/) in for an example. + +Usage +===== + +In order to use AF_XDP sockets there are two parts needed. The +user-space application and the XDP program. For a complete setup and +usage example, please refer to the sample application. The user-space +side is xdpsock_user.c and the XDP side xdpsock_kern.c. + +Naive ring dequeue and enqueue could look like this:: + + // typedef struct xdp_rxtx_ring RING; + // typedef struct xdp_umem_ring RING; + + // typedef struct xdp_desc RING_TYPE; + // typedef __u32 RING_TYPE; + + int dequeue_one(RING *ring, RING_TYPE *item) + { + __u32 entries = ring->ptrs.producer - ring->ptrs.consumer; + + if (entries == 0) + return -1; + + // read-barrier! + + *item = ring->desc[ring->ptrs.consumer & (RING_SIZE - 1)]; + ring->ptrs.consumer++; + return 0; + } + + int enqueue_one(RING *ring, const RING_TYPE *item) + { + u32 free_entries = RING_SIZE - (ring->ptrs.producer - ring->ptrs.consumer); + + if (free_entries == 0) + return -1; + + ring->desc[ring->ptrs.producer & (RING_SIZE - 1)] = *item; + + // write-barrier! + + ring->ptrs.producer++; + return 0; + } + + +For a more optimized version, please refer to the sample application. + +Sample application +================== + +There is a xdpsock benchmarking/test application included that +demonstrates how to use AF_XDP sockets with both private and shared +UMEMs. Say that you would like your UDP traffic from port 4242 to end +up in queue 16, that we will enable AF_XDP on. Here, we use ethtool +for this:: + + ethtool -N p3p2 rx-flow-hash udp4 fn + ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \ + action 16 + +Running the rxdrop benchmark in XDP_DRV mode can then be done +using:: + + samples/bpf/xdpsock -i p3p2 -q 16 -r -N + +For XDP_SKB mode, use the switch "-S" instead of "-N" and all options +can be displayed with "-h", as usual. + +Credits +======= + +- Björn Töpel (AF_XDP core) +- Magnus Karlsson (AF_XDP core) +- Alexander Duyck +- Alexei Starovoitov +- Daniel Borkmann +- Jesper Dangaard Brouer +- John Fastabend +- Jonathan Corbet (LWN coverage) +- Michael S. Tsirkin +- Qi Z Zhang +- Willem de Bruijn + diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt index 9ba04c0bab8d..c13214d073a4 100644 --- a/Documentation/networking/bonding.txt +++ b/Documentation/networking/bonding.txt @@ -140,7 +140,7 @@ bonding module at load time, or are specified via sysfs. Module options may be given as command line arguments to the insmod or modprobe command, but are usually specified in either the -/etc/modrobe.d/*.conf configuration files, or in a distro-specific +/etc/modprobe.d/*.conf configuration files, or in a distro-specific configuration file (some of which are detailed in the next section). Details on bonding support for sysfs is provided in the diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index fd55c7de9991..e6b4ebb2b243 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -483,6 +483,12 @@ Example output from dmesg: [ 3389.935851] JIT code: 00000030: 00 e8 28 94 ff e0 83 f8 01 75 07 b8 ff ff 00 00 [ 3389.935852] JIT code: 00000040: eb 02 31 c0 c9 c3 +When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1 and +setting any other value than that will return in failure. This is even the case for +setting bpf_jit_enable to 2, since dumping the final JIT image into the kernel log +is discouraged and introspection through bpftool (under tools/bpf/bpftool/) is the +generally recommended approach instead. + In the kernel source tree under tools/bpf/, there's bpf_jit_disasm for generating disassembly out of the kernel log's hexdump: @@ -1136,6 +1142,7 @@ into a register from memory, the register's top 56 bits are known zero, while the low 8 are unknown - which is represented as the tnum (0x0; 0xff). If we then OR this with 0x40, we get (0x40; 0xbf), then if we add 1 we get (0x0; 0x1ff), because of potential carries. + Besides arithmetic, the register state can also be updated by conditional branches. For instance, if a SCALAR_VALUE is compared > 8, in the 'true' branch it will have a umin_value (unsigned minimum value) of 9, whereas in the 'false' @@ -1144,14 +1151,16 @@ BPF_JSGE) would instead update the signed minimum/maximum values. Information from the signed and unsigned bounds can be combined; for instance if a value is first tested < 8 and then tested s> 4, the verifier will conclude that the value is also > 4 and s< 8, since the bounds prevent crossing the sign boundary. + PTR_TO_PACKETs with a variable offset part have an 'id', which is common to all pointers sharing that same variable offset. This is important for packet range -checks: after adding some variable to a packet pointer, if you then copy it to -another register and (say) add a constant 4, both registers will share the same -'id' but one will have a fixed offset of +4. Then if it is bounds-checked and -found to be less than a PTR_TO_PACKET_END, the other register is now known to -have a safe range of at least 4 bytes. See 'Direct packet access', below, for -more on PTR_TO_PACKET ranges. +checks: after adding a variable to a packet pointer register A, if you then copy +it to another register B and then add a constant 4 to A, both registers will +share the same 'id' but the A will have a fixed offset of +4. Then if A is +bounds-checked and found to be less than a PTR_TO_PACKET_END, the register B is +now known to have a safe range of at least 4 bytes. See 'Direct packet access', +below, for more on PTR_TO_PACKET ranges. + The 'id' field is also used on PTR_TO_MAP_VALUE_OR_NULL, common to all copies of the pointer returned from a map lookup. This means that when one copy is checked and found to be non-NULL, all copies can become PTR_TO_MAP_VALUEs. diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index f204eaff657d..cbd9bdd4a79e 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -6,6 +6,7 @@ Contents: .. toctree:: :maxdepth: 2 + af_xdp batman-adv can dpaa2/index diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 35ffaa281b26..924bd51327b7 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -449,8 +449,10 @@ tcp_recovery - INTEGER features. RACK: 0x1 enables the RACK loss detection for fast detection of lost - retransmissions and tail drops. + retransmissions and tail drops. It also subsumes and disables + RFC6675 recovery for SACK connections. RACK: 0x2 makes RACK's reordering window static (min_rtt/4). + RACK: 0x4 disables RACK's DUPACK threshold heuristic Default: 0x1 @@ -523,6 +525,19 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max tcp_sack - BOOLEAN Enable select acknowledgments (SACKS). +tcp_comp_sack_delay_ns - LONG INTEGER + TCP tries to reduce number of SACK sent, using a timer + based on 5% of SRTT, capped by this sysctl, in nano seconds. + The default is 1ms, based on TSO autosizing period. + + Default : 1,000,000 ns (1 ms) + +tcp_comp_sack_nr - INTEGER + Max numer of SACK that can be compressed. + Using 0 disables SACK compression. + + Detault : 44 + tcp_slow_start_after_idle - BOOLEAN If set, provide RFC2861 behavior and time out the congestion window after an idle period. An idle period is defined at @@ -1428,6 +1443,19 @@ ip6frag_low_thresh - INTEGER ip6frag_time - INTEGER Time in seconds to keep an IPv6 fragment in memory. +IPv6 Segment Routing: + +seg6_flowlabel - INTEGER + Controls the behaviour of computing the flowlabel of outer + IPv6 header in case of SR T.encaps + + -1 set flowlabel to zero. + 0 copy flowlabel from Inner packet in case of Inner IPv6 + (Set flowlabel to 0 in case IPv4/L2) + 1 Compute the flowlabel using seg6_make_flowlabel() + + Default is 0. + conf/default/*: Change the interface-specific default settings. diff --git a/Documentation/networking/netdev-features.txt b/Documentation/networking/netdev-features.txt index c77f9d57eb91..c4a54c162547 100644 --- a/Documentation/networking/netdev-features.txt +++ b/Documentation/networking/netdev-features.txt @@ -113,6 +113,13 @@ whatever headers there might be. NETIF_F_TSO_ECN means that hardware can properly split packets with CWR bit set, be it TCPv4 (when NETIF_F_TSO is enabled) or TCPv6 (NETIF_F_TSO6). + * Transmit UDP segmentation offload + +NETIF_F_GSO_UDP_GSO_L4 accepts a single UDP header with a payload that exceeds +gso_size. On segmentation, it segments the payload on gso_size boundaries and +replicates the network and UDP headers (fixing up the last one if less than +gso_size). + * Transmit DMA from high memory On platforms where this is relevant, NETIF_F_HIGHDMA signals that |