From 56c07271307b4a20802005692b2b70dfe13d72e8 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Tue, 9 Aug 2011 04:20:48 +0000 Subject: net: add Documentation/networking/scaling.txt Describes RSS, RPS, RFS, accelerated RFS, and XPS. This version incorporates comments by Randy Dunlap and Rick Jones. Besides text cleanup, it adds an explicit "Suggested Configuration" heading to each section. Signed-off-by: Willem de Bruijn Acked-By: Rick Jones Signed-off-by: David S. Miller --- Documentation/networking/scaling.txt | 371 +++++++++++++++++++++++++++++++++++ 1 file changed, 371 insertions(+) create mode 100644 Documentation/networking/scaling.txt (limited to 'Documentation/networking') diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt new file mode 100644 index 000000000000..7254b4b5910e --- /dev/null +++ b/Documentation/networking/scaling.txt @@ -0,0 +1,371 @@ +Scaling in the Linux Networking Stack + + +Introduction +============ + +This document describes a set of complementary techniques in the Linux +networking stack to increase parallelism and improve performance for +multi-processor systems. + +The following technologies are described: + + RSS: Receive Side Scaling + RPS: Receive Packet Steering + RFS: Receive Flow Steering + Accelerated Receive Flow Steering + XPS: Transmit Packet Steering + + +RSS: Receive Side Scaling +========================= + +Contemporary NICs support multiple receive and transmit descriptor queues +(multi-queue). On reception, a NIC can send different packets to different +queues to distribute processing among CPUs. The NIC distributes packets by +applying a filter to each packet that assigns it to one of a small number +of logical flows. Packets for each flow are steered to a separate receive +queue, which in turn can be processed by separate CPUs. This mechanism is +generally known as “Receive-side Scaling” (RSS). The goal of RSS and +the other scaling techniques to increase performance uniformly. +Multi-queue distribution can also be used for traffic prioritization, but +that is not the focus of these techniques. + +The filter used in RSS is typically a hash function over the network +and/or transport layer headers-- for example, a 4-tuple hash over +IP addresses and TCP ports of a packet. The most common hardware +implementation of RSS uses a 128-entry indirection table where each entry +stores a queue number. The receive queue for a packet is determined +by masking out the low order seven bits of the computed hash for the +packet (usually a Toeplitz hash), taking this number as a key into the +indirection table and reading the corresponding value. + +Some advanced NICs allow steering packets to queues based on +programmable filters. For example, webserver bound TCP port 80 packets +can be directed to their own receive queue. Such “n-tuple” filters can +be configured from ethtool (--config-ntuple). + +==== RSS Configuration + +The driver for a multi-queue capable NIC typically provides a kernel +module parameter for specifying the number of hardware queues to +configure. In the bnx2x driver, for instance, this parameter is called +num_queues. A typical RSS configuration would be to have one receive queue +for each CPU if the device supports enough queues, or otherwise at least +one for each cache domain at a particular cache level (L1, L2, etc.). + +The indirection table of an RSS device, which resolves a queue by masked +hash, is usually programmed by the driver at initialization. The +default mapping is to distribute the queues evenly in the table, but the +indirection table can be retrieved and modified at runtime using ethtool +commands (--show-rxfh-indir and --set-rxfh-indir). Modifying the +indirection table could be done to give different queues different +relative weights. + +== RSS IRQ Configuration + +Each receive queue has a separate IRQ associated with it. The NIC triggers +this to notify a CPU when new packets arrive on the given queue. The +signaling path for PCIe devices uses message signaled interrupts (MSI-X), +that can route each interrupt to a particular CPU. The active mapping +of queues to IRQs can be determined from /proc/interrupts. By default, +an IRQ may be handled on any CPU. Because a non-negligible part of packet +processing takes place in receive interrupt handling, it is advantageous +to spread receive interrupts between CPUs. To manually adjust the IRQ +affinity of each interrupt see Documentation/IRQ-affinity. Some systems +will be running irqbalance, a daemon that dynamically optimizes IRQ +assignments and as a result may override any manual settings. + +== Suggested Configuration + +RSS should be enabled when latency is a concern or whenever receive +interrupt processing forms a bottleneck. Spreading load between CPUs +decreases queue length. For low latency networking, the optimal setting +is to allocate as many queues as there are CPUs in the system (or the +NIC maximum, if lower). Because the aggregate number of interrupts grows +with each additional queue, the most efficient high-rate configuration +is likely the one with the smallest number of receive queues where no +CPU that processes receive interrupts reaches 100% utilization. Per-cpu +load can be observed using the mpstat utility. + + +RPS: Receive Packet Steering +============================ + +Receive Packet Steering (RPS) is logically a software implementation of +RSS. Being in software, it is necessarily called later in the datapath. +Whereas RSS selects the queue and hence CPU that will run the hardware +interrupt handler, RPS selects the CPU to perform protocol processing +above the interrupt handler. This is accomplished by placing the packet +on the desired CPU’s backlog queue and waking up the CPU for processing. +RPS has some advantages over RSS: 1) it can be used with any NIC, +2) software filters can easily be added to hash over new protocols, +3) it does not increase hardware device interrupt rate (although it does +introduce inter-processor interrupts (IPIs)). + +RPS is called during bottom half of the receive interrupt handler, when +a driver sends a packet up the network stack with netif_rx() or +netif_receive_skb(). These call the get_rps_cpu() function, which +selects the queue that should process a packet. + +The first step in determining the target CPU for RPS is to calculate a +flow hash over the packet’s addresses or ports (2-tuple or 4-tuple hash +depending on the protocol). This serves as a consistent hash of the +associated flow of the packet. The hash is either provided by hardware +or will be computed in the stack. Capable hardware can pass the hash in +the receive descriptor for the packet; this would usually be the same +hash used for RSS (e.g. computed Toeplitz hash). The hash is saved in +skb->rx_hash and can be used elsewhere in the stack as a hash of the +packet’s flow. + +Each receive hardware queue has an associated list of CPUs to which +RPS may enqueue packets for processing. For each received packet, +an index into the list is computed from the flow hash modulo the size +of the list. The indexed CPU is the target for processing the packet, +and the packet is queued to the tail of that CPU’s backlog queue. At +the end of the bottom half routine, IPIs are sent to any CPUs for which +packets have been queued to their backlog queue. The IPI wakes backlog +processing on the remote CPU, and any queued packets are then processed +up the networking stack. + +==== RPS Configuration + +RPS requires a kernel compiled with the CONFIG_RPS kconfig symbol (on +by default for SMP). Even when compiled in, RPS remains disabled until +explicitly configured. The list of CPUs to which RPS may forward traffic +can be configured for each receive queue using a sysfs file entry: + + /sys/class/net//queues/rx-/rps_cpus + +This file implements a bitmap of CPUs. RPS is disabled when it is zero +(the default), in which case packets are processed on the interrupting +CPU. Documentation/IRQ-affinity.txt explains how CPUs are assigned to +the bitmap. + +== Suggested Configuration + +For a single queue device, a typical RPS configuration would be to set +the rps_cpus to the CPUs in the same cache domain of the interrupting +CPU. If NUMA locality is not an issue, this could also be all CPUs in +the system. At high interrupt rate, it might be wise to exclude the +interrupting CPU from the map since that already performs much work. + +For a multi-queue system, if RSS is configured so that a hardware +receive queue is mapped to each CPU, then RPS is probably redundant +and unnecessary. If there are fewer hardware queues than CPUs, then +RPS might be beneficial if the rps_cpus for each queue are the ones that +share the same cache domain as the interrupting CPU for that queue. + + +RFS: Receive Flow Steering +========================== + +While RPS steers packets solely based on hash, and thus generally +provides good load distribution, it does not take into account +application locality. This is accomplished by Receive Flow Steering +(RFS). The goal of RFS is to increase datacache hitrate by steering +kernel processing of packets to the CPU where the application thread +consuming the packet is running. RFS relies on the same RPS mechanisms +to enqueue packets onto the backlog of another CPU and to wake up that +CPU. + +In RFS, packets are not forwarded directly by the value of their hash, +but the hash is used as index into a flow lookup table. This table maps +flows to the CPUs where those flows are being processed. The flow hash +(see RPS section above) is used to calculate the index into this table. +The CPU recorded in each entry is the one which last processed the flow. +If an entry does not hold a valid CPU, then packets mapped to that entry +are steered using plain RPS. Multiple table entries may point to the +same CPU. Indeed, with many flows and few CPUs, it is very likely that +a single application thread handles flows with many different flow hashes. + +rps_sock_table is a global flow table that contains the *desired* CPU for +flows: the CPU that is currently processing the flow in userspace. Each +table value is a CPU index that is updated during calls to recvmsg and +sendmsg (specifically, inet_recvmsg(), inet_sendmsg(), inet_sendpage() +and tcp_splice_read()). + +When the scheduler moves a thread to a new CPU while it has outstanding +receive packets on the old CPU, packets may arrive out of order. To +avoid this, RFS uses a second flow table to track outstanding packets +for each flow: rps_dev_flow_table is a table specific to each hardware +receive queue of each device. Each table value stores a CPU index and a +counter. The CPU index represents the *current* CPU onto which packets +for this flow are enqueued for further kernel processing. Ideally, kernel +and userspace processing occur on the same CPU, and hence the CPU index +in both tables is identical. This is likely false if the scheduler has +recently migrated a userspace thread while the kernel still has packets +enqueued for kernel processing on the old CPU. + +The counter in rps_dev_flow_table values records the length of the current +CPU's backlog when a packet in this flow was last enqueued. Each backlog +queue has a head counter that is incremented on dequeue. A tail counter +is computed as head counter + queue length. In other words, the counter +in rps_dev_flow_table[i] records the last element in flow i that has +been enqueued onto the currently designated CPU for flow i (of course, +entry i is actually selected by hash and multiple flows may hash to the +same entry i). + +And now the trick for avoiding out of order packets: when selecting the +CPU for packet processing (from get_rps_cpu()) the rps_sock_flow table +and the rps_dev_flow table of the queue that the packet was received on +are compared. If the desired CPU for the flow (found in the +rps_sock_flow table) matches the current CPU (found in the rps_dev_flow +table), the packet is enqueued onto that CPU’s backlog. If they differ, +the current CPU is updated to match the desired CPU if one of the +following is true: + +- The current CPU's queue head counter >= the recorded tail counter + value in rps_dev_flow[i] +- The current CPU is unset (equal to NR_CPUS) +- The current CPU is offline + +After this check, the packet is sent to the (possibly updated) current +CPU. These rules aim to ensure that a flow only moves to a new CPU when +there are no packets outstanding on the old CPU, as the outstanding +packets could arrive later than those about to be processed on the new +CPU. + +==== RFS Configuration + +RFS is only available if the kconfig symbol CONFIG_RFS is enabled (on +by default for SMP). The functionality remains disabled until explicitly +configured. The number of entries in the global flow table is set through: + + /proc/sys/net/core/rps_sock_flow_entries + +The number of entries in the per-queue flow table are set through: + + /sys/class/net//queues/tx-/rps_flow_cnt + +== Suggested Configuration + +Both of these need to be set before RFS is enabled for a receive queue. +Values for both are rounded up to the nearest power of two. The +suggested flow count depends on the expected number of active connections +at any given time, which may be significantly less than the number of open +connections. We have found that a value of 32768 for rps_sock_flow_entries +works fairly well on a moderately loaded server. + +For a single queue device, the rps_flow_cnt value for the single queue +would normally be configured to the same value as rps_sock_flow_entries. +For a multi-queue device, the rps_flow_cnt for each queue might be +configured as rps_sock_flow_entries / N, where N is the number of +queues. So for instance, if rps_flow_entries is set to 32768 and there +are 16 configured receive queues, rps_flow_cnt for each queue might be +configured as 2048. + + +Accelerated RFS +=============== + +Accelerated RFS is to RFS what RSS is to RPS: a hardware-accelerated load +balancing mechanism that uses soft state to steer flows based on where +the application thread consuming the packets of each flow is running. +Accelerated RFS should perform better than RFS since packets are sent +directly to a CPU local to the thread consuming the data. The target CPU +will either be the same CPU where the application runs, or at least a CPU +which is local to the application thread’s CPU in the cache hierarchy. + +To enable accelerated RFS, the networking stack calls the +ndo_rx_flow_steer driver function to communicate the desired hardware +queue for packets matching a particular flow. The network stack +automatically calls this function every time a flow entry in +rps_dev_flow_table is updated. The driver in turn uses a device specific +method to program the NIC to steer the packets. + +The hardware queue for a flow is derived from the CPU recorded in +rps_dev_flow_table. The stack consults a CPU to hardware queue map which +is maintained by the NIC driver. This is an auto-generated reverse map of +the IRQ affinity table shown by /proc/interrupts. Drivers can use +functions in the cpu_rmap (“CPU affinity reverse map”) kernel library +to populate the map. For each CPU, the corresponding queue in the map is +set to be one whose processing CPU is closest in cache locality. + +==== Accelerated RFS Configuration + +Accelerated RFS is only available if the kernel is compiled with +CONFIG_RFS_ACCEL and support is provided by the NIC device and driver. +It also requires that ntuple filtering is enabled via ethtool. The map +of CPU to queues is automatically deduced from the IRQ affinities +configured for each receive queue by the driver, so no additional +configuration should be necessary. + +== Suggested Configuration + +This technique should be enabled whenever one wants to use RFS and the +NIC supports hardware acceleration. + +XPS: Transmit Packet Steering +============================= + +Transmit Packet Steering is a mechanism for intelligently selecting +which transmit queue to use when transmitting a packet on a multi-queue +device. To accomplish this, a mapping from CPU to hardware queue(s) is +recorded. The goal of this mapping is usually to assign queues +exclusively to a subset of CPUs, where the transmit completions for +these queues are processed on a CPU within this set. This choice +provides two benefits. First, contention on the device queue lock is +significantly reduced since fewer CPUs contend for the same queue +(contention can be eliminated completely if each CPU has its own +transmit queue). Secondly, cache miss rate on transmit completion is +reduced, in particular for data cache lines that hold the sk_buff +structures. + +XPS is configured per transmit queue by setting a bitmap of CPUs that +may use that queue to transmit. The reverse mapping, from CPUs to +transmit queues, is computed and maintained for each network device. +When transmitting the first packet in a flow, the function +get_xps_queue() is called to select a queue. This function uses the ID +of the running CPU as a key into the CPU-to-queue lookup table. If the +ID matches a single queue, that is used for transmission. If multiple +queues match, one is selected by using the flow hash to compute an index +into the set. + +The queue chosen for transmitting a particular flow is saved in the +corresponding socket structure for the flow (e.g. a TCP connection). +This transmit queue is used for subsequent packets sent on the flow to +prevent out of order (ooo) packets. The choice also amortizes the cost +of calling get_xps_queues() over all packets in the connection. To avoid +ooo packets, the queue for a flow can subsequently only be changed if +skb->ooo_okay is set for a packet in the flow. This flag indicates that +there are no outstanding packets in the flow, so the transmit queue can +change without the risk of generating out of order packets. The +transport layer is responsible for setting ooo_okay appropriately. TCP, +for instance, sets the flag when all data for a connection has been +acknowledged. + +==== XPS Configuration + +XPS is only available if the kconfig symbol CONFIG_XPS is enabled (on by +default for SMP). The functionality remains disabled until explicitly +configured. To enable XPS, the bitmap of CPUs that may use a transmit +queue is configured using the sysfs file entry: + +/sys/class/net//queues/tx-/xps_cpus + +== Suggested Configuration + +For a network device with a single transmission queue, XPS configuration +has no effect, since there is no choice in this case. In a multi-queue +system, XPS is preferably configured so that each CPU maps onto one queue. +If there are as many queues as there are CPUs in the system, then each +queue can also map onto one CPU, resulting in exclusive pairings that +experience no contention. If there are fewer queues than CPUs, then the +best CPUs to share a given queue are probably those that share the cache +with the CPU that processes transmit completions for that queue +(transmit interrupts). + + +Further Information +=================== +RPS and RFS were introduced in kernel 2.6.35. XPS was incorporated into +2.6.38. Original patches were submitted by Tom Herbert +(therbert@google.com) + +Accelerated RFS was introduced in 2.6.35. Original patches were +submitted by Ben Hutchings (bhutchings@solarflare.com) + +Authors: +Tom Herbert (therbert@google.com) +Willem de Bruijn (willemb@google.com) -- cgit v1.2.2 From b88cf73d9278a5838e3ac2b670ab3b4ff533ea17 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Thu, 11 Aug 2011 14:39:59 +0000 Subject: net: add missing entries to Documentation/networking/00-INDEX A simple janitor duty patch that adds a one sentence overview to 00-INDEX for all files that lacked it. - does not add entries for subdirectories - does not modify existing entries. Signed-off-by: David S. Miller --- Documentation/networking/00-INDEX | 116 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 116 insertions(+) (limited to 'Documentation/networking') diff --git a/Documentation/networking/00-INDEX b/Documentation/networking/00-INDEX index 4edd78dfb362..811252b3da46 100644 --- a/Documentation/networking/00-INDEX +++ b/Documentation/networking/00-INDEX @@ -1,13 +1,21 @@ 00-INDEX - this file +3c359.txt + - information on the 3Com TokenLink Velocity XL (3c5359) driver. 3c505.txt - information on the 3Com EtherLink Plus (3c505) driver. +3c509.txt + - information on the 3Com Etherlink III Series Ethernet cards. 6pack.txt - info on the 6pack protocol, an alternative to KISS for AX.25 DLINK.txt - info on the D-Link DE-600/DE-620 parallel port pocket adapters PLIP.txt - PLIP: The Parallel Line Internet Protocol device driver +README.ipw2100 + - README for the Intel PRO/Wireless 2100 driver. +README.ipw2200 + - README for the Intel PRO/Wireless 2915ABG and 2200BG driver. README.sb1000 - info on General Instrument/NextLevel SURFboard1000 cable modem. alias.txt @@ -20,8 +28,12 @@ atm.txt - info on where to get ATM programs and support for Linux. ax25.txt - info on using AX.25 and NET/ROM code for Linux +batman-adv.txt + - B.A.T.M.A.N routing protocol on top of layer 2 Ethernet Frames. baycom.txt - info on the driver for Baycom style amateur radio modems +bonding.txt + - Linux Ethernet Bonding Driver HOWTO: link aggregation in Linux. bridge.txt - where to get user space programs for ethernet bridging with Linux. can.txt @@ -34,32 +46,60 @@ cxacru.txt - Conexant AccessRunner USB ADSL Modem cxacru-cf.py - Conexant AccessRunner USB ADSL Modem configuration file parser +cxgb.txt + - Release Notes for the Chelsio N210 Linux device driver. +dccp.txt + - the Datagram Congestion Control Protocol (DCCP) (RFC 4340..42). de4x5.txt - the Digital EtherWORKS DE4?? and DE5?? PCI Ethernet driver decnet.txt - info on using the DECnet networking layer in Linux. depca.txt - the Digital DEPCA/EtherWORKS DE1?? and DE2?? LANCE Ethernet driver +dl2k.txt + - README for D-Link DL2000-based Gigabit Ethernet Adapters (dl2k.ko). +dm9000.txt + - README for the Simtec DM9000 Network driver. dmfe.txt - info on the Davicom DM9102(A)/DM9132/DM9801 fast ethernet driver. +dns_resolver.txt + - The DNS resolver module allows kernel servies to make DNS queries. +driver.txt + - Softnet driver issues. e100.txt - info on Intel's EtherExpress PRO/100 line of 10/100 boards e1000.txt - info on Intel's E1000 line of gigabit ethernet boards +e1000e.txt + - README for the Intel Gigabit Ethernet Driver (e1000e). eql.txt - serial IP load balancing ewrk3.txt - the Digital EtherWORKS 3 DE203/4/5 Ethernet driver +fib_trie.txt + - Level Compressed Trie (LC-trie) notes: a structure for routing. filter.txt - Linux Socket Filtering fore200e.txt - FORE Systems PCA-200E/SBA-200E ATM NIC driver info. framerelay.txt - info on using Frame Relay/Data Link Connection Identifier (DLCI). +gen_stats.txt + - Generic networking statistics for netlink users. +generic_hdlc.txt + - The generic High Level Data Link Control (HDLC) layer. generic_netlink.txt - info on Generic Netlink +gianfar.txt + - Gianfar Ethernet Driver. ieee802154.txt - Linux IEEE 802.15.4 implementation, API and drivers +ifenslave.c + - Configure network interfaces for parallel routing (bonding). +igb.txt + - README for the Intel Gigabit Ethernet Driver (igb). +igbvf.txt + - README for the Intel Gigabit Ethernet Driver (igbvf). ip-sysctl.txt - /proc/sys/net/ipv4/* variables ip_dynaddr.txt @@ -68,41 +108,117 @@ ipddp.txt - AppleTalk-IP Decapsulation and AppleTalk-IP Encapsulation iphase.txt - Interphase PCI ATM (i)Chip IA Linux driver info. +ipv6.txt + - Options to the ipv6 kernel module. +ipvs-sysctl.txt + - Per-inode explanation of the /proc/sys/net/ipv4/vs interface. irda.txt - where to get IrDA (infrared) utilities and info for Linux. +ixgb.txt + - README for the Intel 10 Gigabit Ethernet Driver (ixgb). +ixgbe.txt + - README for the Intel 10 Gigabit Ethernet Driver (ixgbe). +ixgbevf.txt + - README for the Intel Virtual Function (VF) Driver (ixgbevf). +l2tp.txt + - User guide to the L2TP tunnel protocol. lapb-module.txt - programming information of the LAPB module. ltpc.txt - the Apple or Farallon LocalTalk PC card driver +mac80211-injection.txt + - HOWTO use packet injection with mac80211 multicast.txt - Behaviour of cards under Multicast +multiqueue.txt + - HOWTO for multiqueue network device support. +netconsole.txt + - The network console module netconsole.ko: configuration and notes. +netdev-features.txt + - Network interface "feature mess and how to get out from it alive". netdevices.txt - info on network device driver functions exported to the kernel. +netif-msg.txt + - Design of the network interface message level setting (NETIF_MSG_*). +nfc.txt + - The Linux Near Field Communication (NFS) subsystem. olympic.txt - IBM PCI Pit/Pit-Phy/Olympic Token Ring driver info. +operstates.txt + - Overview of network interface operational states. +packet_mmap.txt + - User guide to memory mapped packet socket rings (PACKET_[RT]X_RING). +phonet.txt + - The Phonet packet protocol used in Nokia cellular modems. +phy.txt + - The PHY abstraction layer. +pktgen.txt + - User guide to the kernel packet generator (pktgen.ko). policy-routing.txt - IP policy-based routing +ppp_generic.txt + - Information about the generic PPP driver. +proc_net_tcp.txt + - Per inode overview of the /proc/net/tcp and /proc/net/tcp6 interfaces. +radiotap-headers.txt + - Background on radiotap headers. ray_cs.txt - Raylink Wireless LAN card driver info. +rds.txt + - Background on the reliable, ordered datagram delivery method RDS. +regulatory.txt + - Overview of the Linux wireless regulatory infrastructure. +rxrpc.txt + - Guide to the RxRPC protocol. +s2io.txt + - Release notes for Neterion Xframe I/II 10GbE driver. +scaling.txt + - Explanation of network scaling techniques: RSS, RPS, RFS, aRFS, XPS. +sctp.txt + - Notes on the Linux kernel implementation of the SCTP protocol. +secid.txt + - Explanation of the secid member in flow structures. skfp.txt - SysKonnect FDDI (SK-5xxx, Compaq Netelligent) driver info. smc9.txt - the driver for SMC's 9000 series of Ethernet cards smctr.txt - SMC TokenCard TokenRing Linux driver info. +spider-net.txt + - README for the Spidernet Driver (as found in PS3 / Cell BE). +stmmac.txt + - README for the STMicro Synopsys Ethernet driver. +tc-actions-env-rules.txt + - rules for traffic control (tc) actions. +timestamping.txt + - overview of network packet timestamping variants. tcp.txt - short blurb on how TCP output takes place. +tcp-thin.txt + - kernel tuning options for low rate 'thin' TCP streams. tlan.txt - ThunderLAN (Compaq Netelligent 10/100, Olicom OC-2xxx) driver info. tms380tr.txt - SysKonnect Token Ring ISA/PCI adapter driver info. +tproxy.txt + - Transparent proxy support user guide. tuntap.txt - TUN/TAP device driver, allowing user space Rx/Tx of packets. +udplite.txt + - UDP-Lite protocol (RFC 3828) introduction. vortex.txt - info on using 3Com Vortex (3c590, 3c592, 3c595, 3c597) Ethernet cards. +vxge.txt + - README for the Neterion X3100 PCIe Server Adapter. x25.txt - general info on X.25 development. x25-iface.txt - description of the X.25 Packet Layer to LAPB device interface. +xfrm_proc.txt + - description of the statistics package for XFRM. +xfrm_sync.txt + - sync patches for XFRM enable migration of an SA between hosts. +xfrm_sysctl.txt + - description of the XFRM configuration options. z8530drv.txt - info about Linux driver for Z8530 based HDLC cards for AX.25 -- cgit v1.2.2 From 320f24e482e6b390c608c6afec253405f9ab7436 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Thu, 11 Aug 2011 14:41:48 +0000 Subject: net: minor update to Documentation/networking/scaling.txt Incorporate last comments about hyperthreading, interrupt coalescing and the definition of cache domains into the network scaling document scaling.txt Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- Documentation/networking/scaling.txt | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) (limited to 'Documentation/networking') diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt index 7254b4b5910e..58fd7414e6c0 100644 --- a/Documentation/networking/scaling.txt +++ b/Documentation/networking/scaling.txt @@ -52,7 +52,8 @@ module parameter for specifying the number of hardware queues to configure. In the bnx2x driver, for instance, this parameter is called num_queues. A typical RSS configuration would be to have one receive queue for each CPU if the device supports enough queues, or otherwise at least -one for each cache domain at a particular cache level (L1, L2, etc.). +one for each memory domain, where a memory domain is a set of CPUs that +share a particular memory level (L1, L2, NUMA node, etc.). The indirection table of an RSS device, which resolves a queue by masked hash, is usually programmed by the driver at initialization. The @@ -82,11 +83,17 @@ RSS should be enabled when latency is a concern or whenever receive interrupt processing forms a bottleneck. Spreading load between CPUs decreases queue length. For low latency networking, the optimal setting is to allocate as many queues as there are CPUs in the system (or the -NIC maximum, if lower). Because the aggregate number of interrupts grows -with each additional queue, the most efficient high-rate configuration +NIC maximum, if lower). The most efficient high-rate configuration is likely the one with the smallest number of receive queues where no -CPU that processes receive interrupts reaches 100% utilization. Per-cpu -load can be observed using the mpstat utility. +receive queue overflows due to a saturated CPU, because in default +mode with interrupt coalescing enabled, the aggregate number of +interrupts (and thus work) grows with each additional queue. + +Per-cpu load can be observed using the mpstat utility, but note that on +processors with hyperthreading (HT), each hyperthread is represented as +a separate CPU. For interrupt handling, HT has shown no benefit in +initial tests, so limit the number of queues to the number of CPU cores +in the system. RPS: Receive Packet Steering @@ -145,7 +152,7 @@ the bitmap. == Suggested Configuration For a single queue device, a typical RPS configuration would be to set -the rps_cpus to the CPUs in the same cache domain of the interrupting +the rps_cpus to the CPUs in the same memory domain of the interrupting CPU. If NUMA locality is not an issue, this could also be all CPUs in the system. At high interrupt rate, it might be wise to exclude the interrupting CPU from the map since that already performs much work. @@ -154,7 +161,7 @@ For a multi-queue system, if RSS is configured so that a hardware receive queue is mapped to each CPU, then RPS is probably redundant and unnecessary. If there are fewer hardware queues than CPUs, then RPS might be beneficial if the rps_cpus for each queue are the ones that -share the same cache domain as the interrupting CPU for that queue. +share the same memory domain as the interrupting CPU for that queue. RFS: Receive Flow Steering @@ -326,7 +333,7 @@ The queue chosen for transmitting a particular flow is saved in the corresponding socket structure for the flow (e.g. a TCP connection). This transmit queue is used for subsequent packets sent on the flow to prevent out of order (ooo) packets. The choice also amortizes the cost -of calling get_xps_queues() over all packets in the connection. To avoid +of calling get_xps_queues() over all packets in the flow. To avoid ooo packets, the queue for a flow can subsequently only be changed if skb->ooo_okay is set for a packet in the flow. This flag indicates that there are no outstanding packets in the flow, so the transmit queue can -- cgit v1.2.2 From 2d5b2c5ca0d3ebe707386b3add365496460cf918 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Thu, 18 Aug 2011 21:30:37 -0700 Subject: net: netdev-features.txt update to Documentation/networking/00-INDEX MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Update netdev-features.txt entry in 00-INDEX to incorporate feedback by Michał Mirosław. v2: restored tabs that were inadvertently changed to spaces in v1. sorry for the error. Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- Documentation/networking/00-INDEX | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/networking') diff --git a/Documentation/networking/00-INDEX b/Documentation/networking/00-INDEX index 811252b3da46..bbce1215434a 100644 --- a/Documentation/networking/00-INDEX +++ b/Documentation/networking/00-INDEX @@ -135,7 +135,7 @@ multiqueue.txt netconsole.txt - The network console module netconsole.ko: configuration and notes. netdev-features.txt - - Network interface "feature mess and how to get out from it alive". + - Network interface features API description. netdevices.txt - info on network device driver functions exported to the kernel. netif-msg.txt -- cgit v1.2.2