computes ssthresh on regular timeout CA_EVENT_LOSS event. Signed-off-by: Yuchung Cheng <> Acked-by: Neal Cardwell <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2013-03-17tcp: Remove TCPCTChristoph Paasch1-10/+0 TCPCT uses option-number 253, reserved for experimental use and should not be used in production environments. Further, TCPCT does not fully implement RFC 6013. As a nice side-effect, removing TCPCT increases TCP's performance for very short flows: Doing an apache-benchmark with -c 100 -n 100000, sending HTTP-requests for files of 1KB size. before this patch: average (among 7 runs) of 20845.5 Requests/Second after: average (among 7 runs) of 21403.6 Requests/Second Signed-off-by: Christoph Paasch <> Signed-off-by: David S. Miller <> 2013-03-12tcp: TLP loss detection.Nandita Dukkipati1-0/+1 This is the second of the TLP patch series; it augments the basic TLP algorithm with a loss detection scheme. This patch implements a mechanism for loss detection when a Tail loss probe retransmission plugs a hole thereby masking packet loss from the sender. The loss detection algorithm relies on counting TLP dupacks as outlined in Sec. 3 of: The basic idea is: Sender keeps track of TLP "episode" upon retransmission of a TLP packet. An episode ends when the sender receives an ACK above the SND.NXT (tracked by tlp_high_seq) at the time of the episode. We want to make sure that before the episode ends the sender receives a "TLP dupack", indicating that the TLP retransmission was unnecessary, so there was no loss/hole that needed plugging. If the sender gets no TLP dupack before the end of the episode, then it reduces ssthresh and the congestion window, because the TLP packet arriving at the receiver probably plugged a hole. Signed-off-by: Nandita Dukkipati <> Acked-by: Neal Cardwell <> Signed-off-by: David S. Miller <> 2013-03-12tcp: Tail loss probe (TLP)Nandita Dukkipati1-1/+0 This patch series implement the Tail loss probe (TLP) algorithm described in The first patch implements the basic algorithm. TLP's goal is to reduce tail latency of short transactions. It achieves this by converting retransmission timeouts (RTOs) occuring due to tail losses (losses at end of transactions) into fast recovery. TLP transmits one packet in two round-trips when a connection is in Open state and isn't receiving any ACKs. The transmitted packet, aka loss probe, can be either new or a retransmission. When there is tail loss, the ACK from a loss probe triggers FACK/early-retransmit based fast recovery, thus avoiding a costly RTO. In the absence of loss, there is no change in the connection state. PTO stands for probe timeout. It is a timer event indicating that an ACK is overdue and triggers a loss probe packet. The PTO value is set to max(2*SRTT, 10ms) and is adjusted to account for delayed ACK timer when there is only one oustanding packet. TLP Algorithm On transmission of new data in Open state: -> packets_out > 1: schedule PTO in max(2*SRTT, 10ms). -> packets_out == 1: schedule PTO in max(2*RTT, 1.5*RTT + 200ms) -> PTO = min(PTO, RTO) Conditions for scheduling PTO: -> Connection is in Open state. -> Connection is either cwnd limited or no new data to send. -> Number of probes per tail loss episode is limited to one. -> Connection is SACK enabled. When PTO fires: new_segment_exists: -> transmit new segment. -> packets_out++. cwnd remains same. no_new_packet: -> retransmit the last segment. Its ACK triggers FACK or early retransmit based recovery. ACK path: -> rearm RTO at start of ACK processing. -> reschedule PTO if need be. In addition, the patch includes a small variation to the Early Retransmit (ER) algorithm, such that ER and TLP together can in principle recover any N-degree of tail loss through fast recovery. TLP is controlled by the same sysctl as ER, tcp_early_retrans sysctl. tcp_early_retrans==0; disables TLP and ER. ==1; enables RFC5827 ER. ==2; delayed ER. ==3; TLP and delayed ER. [DEFAULT] ==4; TLP only. The TLP patch series have been extensively tested on Google Web servers. It is most effective for short Web trasactions, where it reduced RTOs by 15% and improved HTTP response time (average by 6%, 99th percentile by 10%). The transmitted probes account for <0.5% of the overall transmissions. Signed-off-by: Nandita Dukkipati <> Acked-by: Neal Cardwell <> Acked-by: Yuchung Cheng <> Signed-off-by: David S. Miller <> 2013-03-10tcp: Remove unused tw_cookie_values from tcp_timewait_sockChristoph Paasch1-4/+0 tw_cookie_values is never used in the TCP-stack. It was added by 435cf559f (TCPCT part 1d: define TCP cookie option, extend existing struct's), but already at that time it was not used at all, nor mentioned in the commit-message. Signed-off-by: Christoph Paasch <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2013-02-13tcp: adding a per-socket timestamp offsetAndrey Vagin1-0/+3 This functionality is used for restoring tcp sockets. A tcp timestamp depends on how long a system has been running, so it's differ for each host. The solution is to set a per-socket offset. A per-socket offset for a TIME_WAIT socket is inherited from a proper tcp socket. tcp_request_sock doesn't have a timestamp offset, because the repair mode for them are not implemented. Cc: "David S. Miller" <> Cc: Alexey Kuznetsov <> Cc: James Morris <> Cc: Hideaki YOSHIFUJI <> Cc: Patrick McHardy <> Cc: Eric Dumazet <> Cc: Pavel Emelyanov <> Signed-off-by: Andrey Vagin <> Signed-off-by: David S. Miller <> 2013-02-05tcp: remove Appropriate Byte Count supportStephen Hemminger1-1/+0 TCP Appropriate Byte Count was added by me, but later disabled. There is no point in maintaining it since it is a potential source of bugs and Linux already implements other better window protection heuristics. Signed-off-by: Stephen Hemminger <> Signed-off-by: David S. Miller <> 2012-12-09net: Add support for hardware-offloaded encapsulationJoseph Gasparakis1-0/+10 This patch adds support in the kernel for offloading in the NIC Tx and Rx checksumming for encapsulated packets (such as VXLAN and IP GRE). For Tx encapsulation offload, the driver will need to set the right bits in netdev->hw_enc_features. The protocol driver will have to set the skb->encapsulation bit and populate the inner headers, so the NIC driver will use those inner headers to calculate the csum in hardware. For Rx encapsulation offload, the driver will need to set again the skb->encapsulation flag and the skb->ip_csum to CHECKSUM_UNNECESSARY. In that case the protocol driver should push the decapsulated packet up to the stack, again with CHECKSUM_UNNECESSARY. In ether case, the protocol driver should set the skb->encapsulation flag back to zero. Finally the protocol driver should have NETIF_F_RXCSUM flag set in its features. Signed-off-by: Joseph Gasparakis <> Signed-off-by: Peter P Waskiewicz Jr <> Signed-off-by: Alexander Duyck <> Signed-off-by: David S. Miller <> 2012-10-22tcp: add SYN/data info to TCP_INFOYuchung Cheng1-1/+2 Add a bit TCPI_OPT_SYN_DATA (32) to the socket option TCP_INFO:tcpi_options. It's set if the data in SYN (sent or received) is acked by SYN-ACK. Server or client application can use this information to check Fast Open success rate. Signed-off-by: Yuchung Cheng <> Acked-by: Neal Cardwell <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2012-10-13UAPI: (Scripted) Disintegrate include/linuxDavid Howells1-207/+1 Signed-off-by: David Howells <> Acked-by: Arnd Bergmann <> Acked-by: Thomas Gleixner <> Acked-by: Michael Kerrisk <> Acked-by: Paul E. McKenney <> Acked-by: Dave Jones <> 2012-09-20ipv4: Don't add TCP-code in inet_sock_destructChristoph Paasch1-0/+4 Signed-off-by: Christoph Paasch <> Acked-by: H.K. Jerry Chu <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2012-08-31tcp: TCP Fast Open Server - header & support functionsJerry Chu1-3/+42 This patch adds all the necessary data structure and support functions to implement TFO server side. It also documents a number of flags for the sysctl_tcp_fastopen knob, and adds a few Linux extension MIBs. In addition, it includes the following: 1. a new TCP_FASTOPEN socket option an application must call to supply a max backlog allowed in order to enable TFO on its listener. 2. A number of key data structures: "fastopen_rsk" in tcp_sock - for a big socket to access its request_sock for retransmission and ack processing purpose. It is non-NULL iff 3WHS not completed. "fastopenq" in request_sock_queue - points to a per Fast Open listener data structure "fastopen_queue" to keep track of qlen (# of outstanding Fast Open requests) and max_qlen, among other things. "listener" in tcp_request_sock - to point to the original listener for book-keeping purpose, i.e., to maintain qlen against max_qlen as part of defense against IP spoofing attack. 3. various data structure and functions, many in tcp_fastopen.c, to support server side Fast Open cookie operations, including /proc/sys/net/ipv4/tcp_fastopen_key to allow manual rekeying. Signed-off-by: H.K. Jerry Chu <> Cc: Yuchung Cheng <> Cc: Neal Cardwell <> Cc: Eric Dumazet <> Cc: Tom Herbert <> Signed-off-by: David S. Miller <> 2012-07-23tcp: dont drop MTU reduction indicationsEric Dumazet1-0/+6 ICMP messages generated in output path if frame length is bigger than mtu are actually lost because socket is owned by user (doing the xmit) One example is the ipgre_tunnel_xmit() calling icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu)); We had a similar case fixed in commit a34a101e1e6 (ipv6: disable GSO on sockets hitting dst_allfrag). Problem of such fix is that it relied on retransmit timers, so short tcp sessions paid a too big latency increase price. This patch uses the tcp_release_cb() infrastructure so that MTU reduction messages (ICMP messages) are not lost, and no extra delay is added in TCP transmits. Reported-by: Maciej Żenczykowski <> Diagnosed-by: Neal Cardwell <> Signed-off-by: Eric Dumazet <> Cc: Nandita Dukkipati <> Cc: Tom Herbert <> Cc: Tore Anderson <> Signed-off-by: David S. Miller <> 2012-07-20tcp: improve latencies of timer triggered eventsEric Dumazet1-1/+3 Modern TCP stack highly depends on tcp_write_timer() having a small latency, but current implementation doesn't exactly meet the expectations. When a timer fires but finds the socket is owned by the user, it rearms itself for an additional delay hoping next run will be more successful. tcp_write_timer() for example uses a 50ms delay for next try, and it defeats many attempts to get predictable TCP behavior in term of latencies. Use the recently introduced tcp_release_cb(), so that the user owning the socket will call various handlers right before socket release. This will permit us to post a followup patch to address the tcp_tso_should_defer() syndrome (some deferred packets have to wait RTO timer to be transmitted, while cwnd should allow us to send them sooner) Signed-off-by: Eric Dumazet <> Cc: Tom Herbert <> Cc: Yuchung Cheng <> Cc: Neal Cardwell <> Cc: Nandita Dukkipati <> Cc: H.K. Jerry Chu <> Cc: John Heffner <> Signed-off-by: David S. Miller <> 2012-07-19net-tcp: Fast Open client - cookie-less modeYuchung Cheng1-0/+1 In trusted networks, e.g., intranet, data-center, the client does not need to use Fast Open cookie to mitigate DoS attacks. In cookie-less mode, sendmsg() with MSG_FASTOPEN flag will send SYN-data regardless of cookie availability. Signed-off-by: Yuchung Cheng <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2012-07-19net-tcp: Fast Open client - sending SYN-dataYuchung Cheng1-1/+5 This patch implements sending SYN-data in tcp_connect(). The data is from tcp_sendmsg() with flag MSG_FASTOPEN (implemented in a later patch). The length of the cookie in tcp_fastopen_req, init'd to 0, controls the type of the SYN. If the cookie is not cached (len==0), the host sends data-less SYN with Fast Open cookie request option to solicit a cookie from the remote. If cookie is not available (len > 0), the host sends a SYN-data with Fast Open cookie option. If cookie length is negative, the SYN will not include any Fast Open option (for fall back operations). To deal with middleboxes that may drop SYN with data or experimental TCP option, the SYN-data is only sent once. SYN retransmits do not include data or Fast Open options. The connection will fall back to regular TCP handshake. Signed-off-by: Yuchung Cheng <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2012-07-19net-tcp: Fast Open baseYuchung Cheng1-0/+10 This patch impelements the common code for both the client and server. 1. TCP Fast Open option processing. Since Fast Open does not have an option number assigned by IANA yet, it shares the experiment option code 254 by implementing draft-ietf-tcpm-experimental-options with a 16 bits magic number 0xF989. This enables global experiments without clashing the scarce(2) experimental options available for TCP. When the draft status becomes standard (maybe), the client should switch to the new option number assigned while the server supports both numbers for transistion. 2. The new sysctl tcp_fastopen 3. A place holder init function Signed-off-by: Yuchung Cheng <> Acked-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2012-07-11tcp: TCP Small QueuesEric Dumazet1-0/+9 This introduce TSQ (TCP Small Queues) TSQ goal is to reduce number of TCP packets in xmit queues (qdisc & device queues), to reduce RTT and cwnd bias, part of the bufferbloat problem. sk->sk_wmem_alloc not allowed to grow above a given limit, allowing no more than ~128KB [1] per tcp socket in qdisc/dev layers at a given time. TSO packets are sized/capped to half the limit, so that we have two TSO packets in flight, allowing better bandwidth use. As a side effect, setting the limit to 40000 automatically reduces the standard gso max limit (65536) to 40000/2 : It can help to reduce latencies of high prio packets, having smaller TSO packets. This means we divert sock_wfree() to a tcp_wfree() handler, to queue/send following frames when skb_orphan() [2] is called for the already queued skbs. Results on my dev machines (tg3/ixgbe nics) are really impressive, using standard pfifo_fast, and with or without TSO/GSO. Without reduction of nominal bandwidth, we have reduction of buffering per bulk sender : < 1ms on Gbit (instead of 50ms with TSO) < 8ms on 100Mbit (instead of 132 ms) I no longer have 4 MBytes backlogged in qdisc by a single netperf session, and both side socket autotuning no longer use 4 Mbytes. As skb destructor cannot restart xmit itself ( as qdisc lock might be taken at this point ), we delegate the work to a tasklet. We use one tasklest per cpu for performance reasons. If tasklet finds a socket owned by the user, it sets TSQ_OWNED flag. This flag is tested in a new protocol method called from release_sock(), to eventually send new segments. [1] New /proc/sys/net/ipv4/tcp_limit_output_bytes tunable [2] skb_orphan() is usually called at TX completion time, but some drivers call it in their start_xmit() handler. These drivers should at least use BQL, or else a single TCP session can still fill the whole NIC TX ring, since TSQ will have no effect. Signed-off-by: Eric Dumazet <> Cc: Dave Taht <> Cc: Tom Herbert <> Cc: Matt Mathis <> Cc: Yuchung Cheng <> Cc: Nandita Dukkipati <> Signed-off-by: David S. Miller <> 2012-07-10tcp: Remove tw->tw_peerDavid S. Miller1-1/+0 No longer used. Signed-off-by: David S. Miller <> 2012-06-12Merge git:// S. Miller1-10/+10 Conflicts: MAINTAINERS drivers/net/wireless/iwlwifi/pcie/trans.c The iwlwifi conflict was resolved by keeping the code added in 'net' that turns off the buggy chip feature. The MAINTAINERS conflict was merely overlapping changes, one change updated all the wireless web site URLs and the other changed some GIT trees to be Johannes's instead of John's. Signed-off-by: David S. Miller <> 2012-06-09net: Make linux/tcp.h C++ friendly (trivial)Paul Pluzhnikov1-10/+10 I originally sent this patch to <>, but Jiri Kosina did not feel that this is fully appropriate for the trivial tree. Using linux/tcp.h from C++ results in: cat #include <linux/tcp.h> int main() { } g++ -c In file included from /usr/include/linux/tcp.h:72: error: '__u32 __fswab32(__u32)' cannot appear in a constant-expression /usr/include/linux/tcp.h:72: error: a function call cannot appear in a constant-expression ... Attached trivial patch fixes this problem. Tested: - the above compiles with g++ and - the following program generates the same output before/after the patch: #include <linux/tcp.h> #include <stdio.h> int main () { #define P(a) printf("%s: %08x\n", #a, (int)a) P(TCP_FLAG_CWR); P(TCP_FLAG_ECE); P(TCP_FLAG_URG); P(TCP_FLAG_ACK); P(TCP_FLAG_PSH); P(TCP_FLAG_RST); P(TCP_FLAG_SYN); P(TCP_FLAG_FIN); P(TCP_RESERVED_BITS); P(TCP_DATA_OFFSET); #undef P return 0; } Signed-off-by: Paul Pluzhnikov <> Signed-off-by: David S. Miller <> 2012-06-09[PATCH] tcp: Cache inetpeer in timewait socket, and only when necessary.David S. Miller1-1/+2 Since it's guarenteed that we will access the inetpeer if we're trying to do timewait recycling and TCP options were enabled on the connection, just cache the peer in the timewait socket. In the future, inetpeer lookups will be context dependent (per routing realm), and this helps facilitate that as well. Signed-off-by: David S. Miller <> 2012-05-22Merge branch 'for-linus' of ↵Linus Torvalds1-1/+1 git:// Pull trivial updates from Jiri Kosina: "As usual, it's mostly typo fixes, redundant code elimination and some documentation updates." * 'for-linus' of git:// (57 commits) edac, mips: don't change code that has been removed in edac/mips tree xtensa: Change mail addresses of Hannes Weiner and Oskar Schirmer lib: Change mail address of Oskar Schirmer net: Change mail address of Oskar Schirmer arm/m68k: Change mail address of Sebastian Hess i2c: Change mail address of Oskar Schirmer net: Fix tcp_build_and_update_options comment in struct tcp_sock atomic64_32.h: fix parameter naming mismatch Kconfig: replace "--- help ---" with "---help---" c2port: fix bogus Kconfig "default no" edac: Fix spelling errors. qla1280: Remove redundant NULL check before release_firmware() call remoteproc: remove redundant NULL check before release_firmware() qla2xxx: Remove redundant NULL check before release_firmware() call. aic94xx: Get rid of redundant NULL check before release_firmware() call tehuti: delete redundant NULL check before release_firmware() qlogic: get rid of a redundant test for NULL before call to release_firmware() bna: remove redundant NULL test before release_firmware() tg3: remove redundant NULL test before release_firmware() call typhoon: get rid of redundant conditional before all to release_firmware() ... 2012-05-09net: Fix tcp_build_and_update_options comment in struct tcp_sockKyle McMartin1-1/+1 Noticed this comment didn't get updated when tcp_build_and_update_options was refactored. Signed-off-by: Kyle McMartin <> Signed-off-by: Jiri Kosina <> 2012-05-02tcp: early retransmit: delayed fast retransmitYuchung Cheng1-1/+2 Implementing the advanced early retransmit (sysctl_tcp_early_retrans==2). Delays the fast retransmit by an interval of RTT/4. We borrow the RTO timer to implement the delay. If we receive another ACK or send a new packet, the timer is cancelled and restored to original RTO value offset by time elapsed. When the delayed-ER timer fires, we enter fast recovery and perform fast retransmit. Signed-off-by: Yuchung Cheng <> Acked-by: Neal Cardwell <> Signed-off-by: David S. Miller <> 2012-05-02tcp: early retransmitYuchung Cheng1-0/+1 This patch implements RFC 5827 early retransmit (ER) for TCP. It reduces DUPACK threshold (dupthresh) if outstanding packets are less than 4 to recover losses by fast recovery instead of timeout. While the algorithm is simple, small but frequent network reordering makes this feature dangerous: the connection repeatedly enter false recovery and degrade performance. Therefore we implement a mitigation suggested in the appendix of the RFC that delays entering fast recovery by a small interval, i.e., RTT/4. Currently ER is conservative and is disabled for the rest of the connection after the first reordering event. A large scale web server experiment on the performance impact of ER is summarized in section 6 of the paper "Proportional Rate Reduction for TCP”, IMC 2011. Note that Linux has a similar feature called THIN_DUPACK. The differences are THIN_DUPACK do not mitigate reorderings and is only used after slow start. Currently ER is disabled if THIN_DUPACK is enabled. I would be happy to merge THIN_DUPACK feature with ER if people think it's a good idea. ER is enabled by sysctl_tcp_early_retrans: 0: Disables ER 1: Reduce dupthresh to packets_out - 1 when outstanding packets < 4. 2: (Default) reduce dupthresh like mode 1. In addition, delay entering fast recovery by RTT/4. Note: mode 2 is implemented in the third part of this patch series. Signed-off-by: Yuchung Cheng <> Acked-by: Neal Cardwell <> Signed-off-by: David S. Miller <> 2012-04-26tcp repair: Fix unaligned access when repairing options (v2)Pavel Emelyanov1-0/+5 Don't pick __u8/__u16 values directly from raw pointers, but instead use an array of structures of code:value pairs. This is OK, since the buffer we take options from is not an skb memory, but a user-to-kernel one. For those options which don't require any value now, require this to be zero (for potential future extension of this API). v2: Changed tcp_repair_opt to use two __u32-s as spotted by David Laight. Signed-off-by: Pavel Emelyanov <> Signed-off-by: David S. Miller <> 2012-04-21tcp: Repair connection-time negotiated parametersPavel Emelyanov1-0/+1 There are options, which are set up on a socket while performing TCP handshake. Need to resurrect them on a socket while repairing. A new sockoption accepts a buffer and parses it. The buffer should be CODE:VALUE sequence of bytes, where CODE is standard option code and VALUE is the respective value. Only 4 options should be handled on repaired socket. To read 3 out of 4 of these options the TCP_INFO sockoption can be used. An ability to get the last one (the mss_clamp) was added by the previous patch. Now the restore. Three of these options -- timestamp_ok, mss_clamp and snd_wscale -- are just restored on a coket. The sack_ok flags has 2 issues. First, whether or not to do sacks at all. This flag is just read and set back. No other sack info is saved or restored, since according to the standart and the code dropping all sack-ed segments is OK, the sender will resubmit them again, so after the repair we will probably experience a pause in connection. Next, the fack bit. It's just set back on a socket if the respective sysctl is set. No collected stats about packets flow is preserved. As far as I see (plz, correct me if I'm wrong) the fack-based congestion algorithm survives dropping all of the stats and repairs itself eventually, probably losing the performance for that period. Signed-off-by: Pavel Emelyanov <> Signed-off-by: David S. Miller <> 2012-04-21tcp: Initial repair modePavel Emelyanov1-1/+13 This includes (according the the previous description): * TCP_REPAIR sockoption This one just puts the socket in/out of the repair mode. Allowed for CAP_NET_ADMIN and for closed/establised sockets only. When repair mode is turned off and the socket happens to be in the established state the window probe is sent to the peer to 'unlock' the connection. * TCP_REPAIR_QUEUE sockoption This one sets the queue which we're about to repair. The 'no-queue' is set by default. * TCP_QUEUE_SEQ socoption Sets the write_seq/rcv_nxt of a selected repaired queue. Allowed for TCP_CLOSE-d sockets only. When the socket changes its state the other seq-s are changed by the kernel according to the protocol rules (most of the existing code is actually reused). * Ability to forcibly bind a socket to a port The sk->sk_reuse is set to SK_FORCE_REUSE. * Immediate connect modification The connect syscall initializes the connection, then directly jumps to the code which finalizes it. * Silent close modification The close just aborts the connection (similar to SO_LINGER with 0 time) but without sending any FIN/RST-s to peer. Signed-off-by: Pavel Emelyanov <> Signed-off-by: David S. Miller <> 2012-03-01Merge git:// S. Miller1-1/+2 Conflicts: drivers/net/ethernet/broadcom/tg3.c Conflicts in the statistics regression bug fix from 'net', but happily Matt Carlson originally posted the fix against 'net-next' so I used that to resolve this. Signed-off-by: David S. Miller <> 2012-02-28tcp: fix comment for tp->highest_sackNeal Cardwell1-1/+2 There was an off-by-one error in the comments describing the highest_sack field in struct tcp_sock. The comments previously claimed that it was the "start sequence of the highest skb with SACKed bit". This commit fixes the comments to note that it is the "start sequence of the skb just *after* the highest skb with SACKed bit". Signed-off-by: Neal Cardwell <> Acked-by: Ilpo Järvinen <> Signed-off-by: David S. Miller <> 2012-02-01tcp: md5: protects md5sig_info with RCUEric Dumazet1-1/+1 This patch makes sure we use appropriate memory barriers before publishing tp->md5sig_info, allowing tcp_md5_do_lookup() being used from tcp_v4_send_reset() without holding socket lock (upcoming patch from Shawn Lu) Note we also need to respect rcu grace period before its freeing, since we can free socket without this grace period thanks to SLAB_DESTROY_BY_RCU Signed-off-by: Eric Dumazet <> Cc: Shawn Lu <> Signed-off-by: David S. Miller <> 2012-01-31tcp: md5: rcu conversionEric Dumazet1-2/+1 In order to be able to support proper RST messages for TCP MD5 flows, we need to allow access to MD5 keys without locking listener socket. This conversion is a nice cleanup, and shrinks size of timewait sockets by 80 bytes. IPv6 code reuses generic code found in IPv4 instead of duplicating it. Control path uses GFP_KERNEL allocations instead of GFP_ATOMIC. Signed-off-by: Eric Dumazet <> Cc: Shawn Lu <> Signed-off-by: David S. Miller <> 2011-12-21tcp: Replace constants with #define macrosVijay Subramanian1-0/+5 to record the state of SACK/FACK and DSACK for better readability and maintenance. Signed-off-by: Vijay Subramanian <> Signed-off-by: David S. Miller <> 2011-10-03tcp: report ECN_SEEN in tcp_infoEric Dumazet1-1/+2 Allows ss command (iproute2) to display "ecnseen" if at least one packet with ECT(0) or ECT(1) or ECN was received by this socket. "ecn" means ECN was negotiated at session establishment (TCP level) "ecnseen" means we received at least one packet with ECT fields set (IP level) ss -i ... ESTAB 0 0 ino:5950 sk:f178e400 mem:(r0,w0,f0,t0) ts sack ecn ecnseen bic wscale:7,8 rto:210 rtt:12.5/7.5 cwnd:10 send 9.3Mbps rcv_space:14480 Signed-off-by: Eric Dumazet <> Signed-off-by: David S. Miller <> 2011-08-24Proportional Rate Reduction for TCP.Nandita Dukkipati1-0/+4 This patch implements Proportional Rate Reduction (PRR) for TCP. PRR is an algorithm that determines TCP's sending rate in fast recovery. PRR avoids excessive window reductions and aims for the actual congestion window size at the end of recovery to be as close as possible to the window determined by the congestion control algorithm. PRR also improves accuracy of the amount of data sent during loss recovery. The patch implements the recommended flavor of PRR called PRR-SSRB (Proportional rate reduction with slow start reduction bound) and replaces the existing rate halving algorithm. PRR improves upon the existing Linux fast recovery under a number of conditions including: 1) burst losses where the losses implicitly reduce the amount of outstanding data (pipe) below the ssthresh value selected by the congestion control algorithm and, 2) losses near the end of short flows where application runs out of data to send. As an example, with the existing rate halving implementation a single loss event can cause a connection carrying short Web transactions to go into the slow start mode after the recovery. This is because during recovery Linux pulls the congestion window down to packets_in_flight+1 on every ACK. A short Web response often runs out of new data to send and its pipe reduces to zero by the end of recovery when all its packets are drained from the network. Subsequent HTTP responses using the same connection will have to slow start to raise cwnd to ssthresh. PRR on the other hand aims for the cwnd to be as close as possible to ssthresh by the end of recovery. A description of PRR and a discussion of its performance can be found at the following links: - IETF Draft: - IETF Slides: - Paper to appear in Internet Measurements Conference (IMC) 2011: Improving TCP Loss Recovery Nandita Dukkipati, Matt Mathis, Yuchung Cheng Signed-off-by: Nandita Dukkipati <> Signed-off-by: David S. Miller <> 2011-06-08tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open sideJerry Chu1-0/+1 This patch lowers the default initRTO from 3secs to 1sec per RFC2988bis. It falls back to 3secs if the SYN or SYN-ACK packet has been retransmitted, AND the TCP timestamp option is not on. It also adds support to take RTT sample during 3WHS on the passive open side, just like its active open counterpart, and uses it, if valid, to seed the initRTO for the data transmission phase. The patch also resets ssthresh to its initial default at the beginning of the data transmission phase, and reduces cwnd to 1 if there has been MORE THAN ONE retransmission during 3WHS per RFC5681. Signed-off-by: H.K. Jerry Chu <> Signed-off-by: David S. Miller <>