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* net: tcp: move GRO/GSO functions to tcp_offloadDaniel Borkmann2013-06-071-4/+5
| | | | | | | | | | | | | Would be good to make things explicit and move those functions to a new file called tcp_offload.c, thus make this similar to tcpv6_offload.c. While moving all related functions into tcp_offload.c, we can also make some of them static, since they are only used there. Also, add an explicit registration function. Suggested-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: md5: remove spinlock usage in fast pathEric Dumazet2013-05-201-3/+5
| | | | | | | | | | | | | | | | | | TCP md5 code uses per cpu variables but protects access to them with a shared spinlock, which is a contention point. [ tcp_md5sig_pool_lock is locked twice per incoming packet ] Makes things much simpler, by allocating crypto structures once, first time a socket needs md5 keys, and not deallocating them as they are really small. Next step would be to allow crypto allocations being done in a NUMA aware way. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: remove bad timeout logic in fast recoveryYuchung Cheng2013-05-201-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | tcp_timeout_skb() was intended to trigger fast recovery on timeout, unfortunately in reality it often causes spurious retransmission storms during fast recovery. The particular sign is a fast retransmit over the highest sacked sequence (SND.FACK). Currently the RTO timer re-arming (as in RFC6298) offers a nice cushion to avoid spurious timeout: when SND.UNA advances the sender re-arms RTO and extends the timeout by icsk_rto. The sender does not offset the time elapsed since the packet at SND.UNA was sent. But if the next (DUP)ACK arrives later than ~RTTVAR and triggers tcp_fastretrans_alert(), then tcp_timeout_skb() will mark any packet sent before the icsk_rto interval lost, including one that's above the highest sacked sequence. Most likely a large part of scorebard will be marked. If most packets are not lost then the subsequent DUPACKs with new SACK blocks will cause the sender to continue to retransmit packets beyond SND.FACK spuriously. Even if only one packet is lost the sender may falsely retransmit almost the entire window. The situation becomes common in the world of bufferbloat: the RTT continues to grow as the queue builds up but RTTVAR remains small and close to the minimum 200ms. If a data packet is lost and the DUPACK triggered by the next data packet is slightly delayed, then a spurious retransmission storm forms. As the original comment on tcp_timeout_skb() suggests: the usefulness of this feature is questionable. It also wastes cycles walking the sack scoreboard and is actually harmful because of false recovery. It's time to remove this. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Nandita Dukkipati <nanditad@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: GSO should be TSQ friendlyEric Dumazet2013-04-131-0/+1
| | | | | | | | | | | | | | | | | | | | I noticed that TSQ (TCP Small queues) was less effective when TSO is turned off, and GSO is on. If BQL is not enabled, TSQ has then no effect. It turns out the GSO engine frees the original gso_skb at the time the fragments are generated and queued to the NIC. We should instead call the tcp_wfree() destructor for the last fragment, to keep the flow control as intended in TSQ. This effectively limits the number of queued packets on qdisc + NIC layers. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Tom Herbert <therbert@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Nandita Dukkipati <nanditad@google.com> Cc: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Remove dead sysctl_tcp_cookie_size declarationNeal Cardwell2013-04-021-1/+0
| | | | | | | | Remove a declaration left over from the TCPCT-ectomy. This sysctl is no longer referenced anywhere since 1a2c6181c4 ("tcp: Remove TCPCT"). Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: refactor F-RTOYuchung Cheng2013-03-211-4/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The patch series refactor the F-RTO feature (RFC4138/5682). This is to simplify the loss recovery processing. Existing F-RTO was developed during the experimental stage (RFC4138) and has many experimental features. It takes a separate code path from the traditional timeout processing by overloading CA_Disorder instead of using CA_Loss state. This complicates CA_Disorder state handling because it's also used for handling dubious ACKs and undos. While the algorithm in the RFC does not change the congestion control, the implementation intercepts congestion control in various places (e.g., frto_cwnd in tcp_ack()). The new code implements newer F-RTO RFC5682 using CA_Loss processing path. F-RTO becomes a small extension in the timeout processing and interfaces with congestion control and Eifel undo modules. It lets congestion control (module) determines how many to send independently. F-RTO only chooses what to send in order to detect spurious retranmission. If timeout is found spurious it invokes existing Eifel undo algorithms like DSACK or TCP timestamp based detection. The first patch removes all F-RTO code except the sysctl_tcp_frto is left for the new implementation. Since CA_EVENT_FRTO is removed, TCP westwood now computes ssthresh on regular timeout CA_EVENT_LOSS event. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Remove TCPCTChristoph Paasch2013-03-171-88/+1
| | | | | | | | | | | | | | | | | | | | 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 <christoph.paasch@uclouvain.be> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Tail loss probe (TLP)Nandita Dukkipati2013-03-121-2/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch series implement the Tail loss probe (TLP) algorithm described in http://tools.ietf.org/html/draft-dukkipati-tcpm-tcp-loss-probe-01. 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 <nanditad@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: uninline tcp_prequeue()Eric Dumazet2013-03-071-44/+1
| | | | | | | tcp_prequeue() became too big to be inlined. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: avoid wakeups for pure ACKEric Dumazet2013-02-281-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | TCP prequeue mechanism purpose is to let incoming packets being processed by the thread currently blocked in tcp_recvmsg(), instead of behalf of the softirq handler, to better adapt flow control on receiver host capacity to schedule the consumer. But in typical request/answer workloads, we send request, then block to receive the answer. And before the actual answer, TCP stack receives the ACK packets acknowledging the request. Processing pure ACK on behalf of the thread blocked in tcp_recvmsg() is a waste of resources, as thread has to immediately sleep again because it got no payload. This patch avoids the extra context switches and scheduler overhead. Before patch : a:~# echo 0 >/proc/sys/net/ipv4/tcp_low_latency a:~# perf stat ./super_netperf 300 -t TCP_RR -l 10 -H 7.7.7.84 -- -r 8k,8k 231676 Performance counter stats for './super_netperf 300 -t TCP_RR -l 10 -H 7.7.7.84 -- -r 8k,8k': 116251.501765 task-clock # 11.369 CPUs utilized 5,025,463 context-switches # 0.043 M/sec 1,074,511 CPU-migrations # 0.009 M/sec 216,923 page-faults # 0.002 M/sec 311,636,972,396 cycles # 2.681 GHz 260,507,138,069 stalled-cycles-frontend # 83.59% frontend cycles idle 155,590,092,840 stalled-cycles-backend # 49.93% backend cycles idle 100,101,255,411 instructions # 0.32 insns per cycle # 2.60 stalled cycles per insn 16,535,930,999 branches # 142.243 M/sec 646,483,591 branch-misses # 3.91% of all branches 10.225482774 seconds time elapsed After patch : a:~# echo 0 >/proc/sys/net/ipv4/tcp_low_latency a:~# perf stat ./super_netperf 300 -t TCP_RR -l 10 -H 7.7.7.84 -- -r 8k,8k 233297 Performance counter stats for './super_netperf 300 -t TCP_RR -l 10 -H 7.7.7.84 -- -r 8k,8k': 91084.870855 task-clock # 8.887 CPUs utilized 2,485,916 context-switches # 0.027 M/sec 815,520 CPU-migrations # 0.009 M/sec 216,932 page-faults # 0.002 M/sec 245,195,022,629 cycles # 2.692 GHz 202,635,777,041 stalled-cycles-frontend # 82.64% frontend cycles idle 124,280,372,407 stalled-cycles-backend # 50.69% backend cycles idle 83,457,289,618 instructions # 0.34 insns per cycle # 2.43 stalled cycles per insn 13,431,472,361 branches # 147.461 M/sec 504,470,665 branch-misses # 3.76% of all branches 10.249594448 seconds time elapsed Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Tom Herbert <therbert@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Andi Kleen <ak@linux.intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: remove Appropriate Byte Count supportStephen Hemminger2013-02-051-1/+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 <stephen@networkplumber.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: make sysctl_tcp_ecn namespace awareHannes Frederic Sowa2013-01-071-4/+5
| | | | | | | | | | | | | | As per suggestion from Eric Dumazet this patch makes tcp_ecn sysctl namespace aware. The reason behind this patch is to ease the testing of ecn problems on the internet and allows applications to tune their own use of ecn. Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Cc: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-nextLinus Torvalds2012-12-131-1/+0
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Pull networking changes from David Miller: 1) Allow to dump, monitor, and change the bridge multicast database using netlink. From Cong Wang. 2) RFC 5961 TCP blind data injection attack mitigation, from Eric Dumazet. 3) Networking user namespace support from Eric W. Biederman. 4) tuntap/virtio-net multiqueue support by Jason Wang. 5) Support for checksum offload of encapsulated packets (basically, tunneled traffic can still be checksummed by HW). From Joseph Gasparakis. 6) Allow BPF filter access to VLAN tags, from Eric Dumazet and Daniel Borkmann. 7) Bridge port parameters over netlink and BPDU blocking support from Stephen Hemminger. 8) Improve data access patterns during inet socket demux by rearranging socket layout, from Eric Dumazet. 9) TIPC protocol updates and cleanups from Ying Xue, Paul Gortmaker, and Jon Maloy. 10) Update TCP socket hash sizing to be more in line with current day realities. The existing heurstics were choosen a decade ago. From Eric Dumazet. 11) Fix races, queue bloat, and excessive wakeups in ATM and associated drivers, from Krzysztof Mazur and David Woodhouse. 12) Support DOVE (Distributed Overlay Virtual Ethernet) extensions in VXLAN driver, from David Stevens. 13) Add "oops_only" mode to netconsole, from Amerigo Wang. 14) Support set and query of VEB/VEPA bridge mode via PF_BRIDGE, also allow DCB netlink to work on namespaces other than the initial namespace. From John Fastabend. 15) Support PTP in the Tigon3 driver, from Matt Carlson. 16) tun/vhost zero copy fixes and improvements, plus turn it on by default, from Michael S. Tsirkin. 17) Support per-association statistics in SCTP, from Michele Baldessari. And many, many, driver updates, cleanups, and improvements. Too numerous to mention individually. * git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next: (1722 commits) net/mlx4_en: Add support for destination MAC in steering rules net/mlx4_en: Use generic etherdevice.h functions. net: ethtool: Add destination MAC address to flow steering API bridge: add support of adding and deleting mdb entries bridge: notify mdb changes via netlink ndisc: Unexport ndisc_{build,send}_skb(). uapi: add missing netconf.h to export list pkt_sched: avoid requeues if possible solos-pci: fix double-free of TX skb in DMA mode bnx2: Fix accidental reversions. bna: Driver Version Updated to 3.1.2.1 bna: Firmware update bna: Add RX State bna: Rx Page Based Allocation bna: TX Intr Coalescing Fix bna: Tx and Rx Optimizations bna: Code Cleanup and Enhancements ath9k: check pdata variable before dereferencing it ath5k: RX timestamp is reported at end of frame ath9k_htc: RX timestamp is reported at end of frame ...
| * tcp: remove dead prototype for tcp_v4_get_peer()Neal Cardwell2012-11-231-1/+0
| | | | | | | | | | | | | | This function no longer exists. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | tcp: bug fix Fast Open client retransmissionYuchung Cheng2012-12-071-0/+1
|/ | | | | | | | | | | | | | | | | | | | If SYN-ACK partially acks SYN-data, the client retransmits the remaining data by tcp_retransmit_skb(). This increments lost recovery state variables like tp->retrans_out in Open state. If loss recovery happens before the retransmission is acked, it triggers the WARN_ON check in tcp_fastretrans_alert(). For example: the client sends SYN-data, gets SYN-ACK acking only ISN, retransmits data, sends another 4 data packets and get 3 dupacks. Since the retransmission is not caused by network drop it should not update the recovery state variables. Further the server may return a smaller MSS than the cached MSS used for SYN-data, so the retranmission needs a loop. Otherwise some data will not be retransmitted until timeout or other loss recovery events. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: TCP Fast Open Server - take SYNACK RTT after completing 3WHSNeal Cardwell2012-09-221-0/+1
| | | | | | | | | | | | | | | | | | | | | When taking SYNACK RTT samples for servers using TCP Fast Open, fix the code to ensure that we only call tcp_valid_rtt_meas() after we receive the ACK that completes the 3-way handshake. Previously we were always taking an RTT sample in tcp_v4_syn_recv_sock(). However, for TCP Fast Open connections tcp_v4_conn_req_fastopen() calls tcp_v4_syn_recv_sock() at the time we receive the SYN. So for TFO we must wait until tcp_rcv_state_process() to take the RTT sample. To fix this, we wait until after TFO calls tcp_v4_syn_recv_sock() before we set the snt_synack timestamp, since tcp_synack_rtt_meas() already ensures that we only take a SYNACK RTT sample if snt_synack is non-zero. To be careful, we only take a snt_synack timestamp when a SYNACK transmit or retransmit succeeds. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: extract code to compute SYNACK RTTNeal Cardwell2012-09-221-0/+9
| | | | | | | | In preparation for adding another spot where we compute the SYNACK RTT, extract this code so that it can be shared. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: use PRR to reduce cwin in CWR stateYuchung Cheng2012-09-031-2/+8
| | | | | | | | | | | | | | | | | | | | | Use proportional rate reduction (PRR) algorithm to reduce cwnd in CWR state, in addition to Recovery state. Retire the current rate-halving in CWR. When losses are detected via ACKs in CWR state, the sender enters Recovery state but the cwnd reduction continues and does not restart. Rename and refactor cwnd reduction functions since both CWR and Recovery use the same algorithm: tcp_init_cwnd_reduction() is new and initiates reduction state variables. tcp_cwnd_reduction() is previously tcp_update_cwnd_in_recovery(). tcp_ends_cwnd_reduction() is previously tcp_complete_cwr(). The rate halving functions and logic such as tcp_cwnd_down(), tcp_min_cwnd(), and the cwnd moderation inside tcp_enter_cwr() are removed. The unused parameter, flag, in tcp_cwnd_reduction() is also removed. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: TCP Fast Open Server - support TFO listenersJerry Chu2012-09-011-2/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch builds on top of the previous patch to add the support for TFO listeners. This includes - 1. allocating, properly initializing, and managing the per listener fastopen_queue structure when TFO is enabled 2. changes to the inet_csk_accept code to support TFO. E.g., the request_sock can no longer be freed upon accept(), not until 3WHS finishes 3. allowing a TCP_SYN_RECV socket to properly poll() and sendmsg() if it's a TFO socket 4. properly closing a TFO listener, and a TFO socket before 3WHS finishes 5. supporting TCP_FASTOPEN socket option 6. modifying tcp_check_req() to use to check a TFO socket as well as request_sock 7. supporting TCP's TFO cookie option 8. adding a new SYN-ACK retransmit handler to use the timer directly off the TFO socket rather than the listener socket. Note that TFO server side will not retransmit anything other than SYN-ACK until the 3WHS is completed. The patch also contains an important function "reqsk_fastopen_remove()" to manage the somewhat complex relation between a listener, its request_sock, and the corresponding child socket. See the comment above the function for the detail. Signed-off-by: H.K. Jerry Chu <hkchu@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Tom Herbert <therbert@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: TCP Fast Open Server - header & support functionsJerry Chu2012-09-011-7/+39
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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 <hkchu@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Tom Herbert <therbert@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Increase timeout for SYN segmentsAlex Bergmann2012-08-311-4/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 9ad7c049 ("tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open side") changed the initRTO from 3secs to 1sec in accordance to RFC6298 (former RFC2988bis). This reduced the time till the last SYN retransmission packet gets sent from 93secs to 31secs. RFC1122 is stating that the retransmission should be done for at least 3 minutes, but this seems to be quite high. "However, the values of R1 and R2 may be different for SYN and data segments. In particular, R2 for a SYN segment MUST be set large enough to provide retransmission of the segment for at least 3 minutes. The application can close the connection (i.e., give up on the open attempt) sooner, of course." This patch increases the value of TCP_SYN_RETRIES to the value of 6, providing a retransmission window of 63secs. The comments for SYN and SYNACK retries have also been updated to describe the current settings. The same goes for the documentation file "Documentation/networking/ip-sysctl.txt". Signed-off-by: Alexander Bergmann <alex@linlab.net> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* Merge branch 'for-next' of ↵David S. Miller2012-08-251-1/+2
|\ | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace This is an initial merge in of Eric Biederman's work to start adding user namespace support to the networking. Signed-off-by: David S. Miller <davem@davemloft.net>
| * userns: Print out socket uids in a user namespace aware fashion.Eric W. Biederman2012-08-151-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Cc: James Morris <jmorris@namei.org> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org> Cc: Patrick McHardy <kaber@trash.net> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net> Cc: Sridhar Samudrala <sri@us.ibm.com> Acked-by: Vlad Yasevich <vyasevich@gmail.com> Acked-by: David S. Miller <davem@davemloft.net> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
* | net: tcp: ipv6_mapped needs sk_rx_dst_set methodEric Dumazet2012-08-101-0/+1
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit 5d299f3d3c8a2fb (net: ipv6: fix TCP early demux) added a regression for ipv6_mapped case. [ 67.422369] SELinux: initialized (dev autofs, type autofs), uses genfs_contexts [ 67.449678] SELinux: initialized (dev autofs, type autofs), uses genfs_contexts [ 92.631060] BUG: unable to handle kernel NULL pointer dereference at (null) [ 92.631435] IP: [< (null)>] (null) [ 92.631645] PGD 0 [ 92.631846] Oops: 0010 [#1] SMP [ 92.632095] Modules linked in: autofs4 sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_multipath dm_mod video sbs sbshc battery ac lp parport sg snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device pcspkr snd_pcm_oss snd_mixer_oss snd_pcm snd_timer serio_raw button floppy snd i2c_i801 i2c_core soundcore snd_page_alloc shpchp ide_cd_mod cdrom microcode ehci_hcd ohci_hcd uhci_hcd [ 92.634294] CPU 0 [ 92.634294] Pid: 4469, comm: sendmail Not tainted 3.6.0-rc1 #3 [ 92.634294] RIP: 0010:[<0000000000000000>] [< (null)>] (null) [ 92.634294] RSP: 0018:ffff880245fc7cb0 EFLAGS: 00010282 [ 92.634294] RAX: ffffffffa01985f0 RBX: ffff88024827ad00 RCX: 0000000000000000 [ 92.634294] RDX: 0000000000000218 RSI: ffff880254735380 RDI: ffff88024827ad00 [ 92.634294] RBP: ffff880245fc7cc8 R08: 0000000000000001 R09: 0000000000000000 [ 92.634294] R10: 0000000000000000 R11: ffff880245fc7bf8 R12: ffff880254735380 [ 92.634294] R13: ffff880254735380 R14: 0000000000000000 R15: 7fffffffffff0218 [ 92.634294] FS: 00007f4516ccd6f0(0000) GS:ffff880256600000(0000) knlGS:0000000000000000 [ 92.634294] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 92.634294] CR2: 0000000000000000 CR3: 0000000245ed1000 CR4: 00000000000007f0 [ 92.634294] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 92.634294] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 92.634294] Process sendmail (pid: 4469, threadinfo ffff880245fc6000, task ffff880254b8cac0) [ 92.634294] Stack: [ 92.634294] ffffffff813837a7 ffff88024827ad00 ffff880254b6b0e8 ffff880245fc7d68 [ 92.634294] ffffffff81385083 00000000001d2680 ffff8802547353a8 ffff880245fc7d18 [ 92.634294] ffffffff8105903a ffff88024827ad60 0000000000000002 00000000000000ff [ 92.634294] Call Trace: [ 92.634294] [<ffffffff813837a7>] ? tcp_finish_connect+0x2c/0xfa [ 92.634294] [<ffffffff81385083>] tcp_rcv_state_process+0x2b6/0x9c6 [ 92.634294] [<ffffffff8105903a>] ? sched_clock_cpu+0xc3/0xd1 [ 92.634294] [<ffffffff81059073>] ? local_clock+0x2b/0x3c [ 92.634294] [<ffffffff8138caf3>] tcp_v4_do_rcv+0x63a/0x670 [ 92.634294] [<ffffffff8133278e>] release_sock+0x128/0x1bd [ 92.634294] [<ffffffff8139f060>] __inet_stream_connect+0x1b1/0x352 [ 92.634294] [<ffffffff813325f5>] ? lock_sock_nested+0x74/0x7f [ 92.634294] [<ffffffff8104b333>] ? wake_up_bit+0x25/0x25 [ 92.634294] [<ffffffff813325f5>] ? lock_sock_nested+0x74/0x7f [ 92.634294] [<ffffffff8139f223>] ? inet_stream_connect+0x22/0x4b [ 92.634294] [<ffffffff8139f234>] inet_stream_connect+0x33/0x4b [ 92.634294] [<ffffffff8132e8cf>] sys_connect+0x78/0x9e [ 92.634294] [<ffffffff813fd407>] ? sysret_check+0x1b/0x56 [ 92.634294] [<ffffffff81088503>] ? __audit_syscall_entry+0x195/0x1c8 [ 92.634294] [<ffffffff811cc26e>] ? trace_hardirqs_on_thunk+0x3a/0x3f [ 92.634294] [<ffffffff813fd3e2>] system_call_fastpath+0x16/0x1b [ 92.634294] Code: Bad RIP value. [ 92.634294] RIP [< (null)>] (null) [ 92.634294] RSP <ffff880245fc7cb0> [ 92.634294] CR2: 0000000000000000 [ 92.648982] ---[ end trace 24e2bed94314c8d9 ]--- [ 92.649146] Kernel panic - not syncing: Fatal exception in interrupt Fix this using inet_sk_rx_dst_set(), and export this function in case IPv6 is modular. Reported-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: improve latencies of timer triggered eventsEric Dumazet2012-07-201-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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 <edumazet@google.com> Cc: Tom Herbert <therbert@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Nandita Dukkipati <nanditad@google.com> Cc: H.K. Jerry Chu <hkchu@google.com> Cc: John Heffner <johnwheffner@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open client - cookie-less modeYuchung Cheng2012-07-191-0/+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 <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open client - detecting SYN-data dropsYuchung Cheng2012-07-191-2/+4
| | | | | | | | | | | | | | | | | | On paths with firewalls dropping SYN with data or experimental TCP options, Fast Open connections will have experience SYN timeout and bad performance. The solution is to track such incidents in the cookie cache and disables Fast Open temporarily. Since only the original SYN includes data and/or Fast Open option, the SYN-ACK has some tell-tale sign (tcp_rcv_fastopen_synack()) to detect such drops. If a path has recurring Fast Open SYN drops, Fast Open is disabled for 2^(recurring_losses) minutes starting from four minutes up to roughly one and half day. sendmsg with MSG_FASTOPEN flag will succeed but it behaves as connect() then write(). Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open client - sendmsg(MSG_FASTOPEN)Yuchung Cheng2012-07-191-0/+3
| | | | | | | | | | | | | | | | | | | | | | | | | sendmsg() (or sendto()) with MSG_FASTOPEN is a combo of connect(2) and write(2). The application should replace connect() with it to send data in the opening SYN packet. For blocking socket, sendmsg() blocks until all the data are buffered locally and the handshake is completed like connect() call. It returns similar errno like connect() if the TCP handshake fails. For non-blocking socket, it returns the number of bytes queued (and transmitted in the SYN-data packet) if cookie is available. If cookie is not available, it transmits a data-less SYN packet with Fast Open cookie request option and returns -EINPROGRESS like connect(). Using MSG_FASTOPEN on connecting or connected socket will result in simlar errno like repeating connect() calls. Therefore the application should only use this flag on new sockets. The buffer size of sendmsg() is independent of the MSS of the connection. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open client - sending SYN-dataYuchung Cheng2012-07-191-0/+9
| | | | | | | | | | | | | | | | | | | | | 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 <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open client - cookie cacheYuchung Cheng2012-07-191-0/+4
| | | | | | | | | | With help from Eric Dumazet, add Fast Open metrics in tcp metrics cache. The basic ones are MSS and the cookies. Later patch will cache more to handle unfriendly middleboxes. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net-tcp: Fast Open baseYuchung Cheng2012-07-191-1/+8
| | | | | | | | | | | | | | | | | | | | | | 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 <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: implement RFC 5961 3.2Eric Dumazet2012-07-171-0/+1
| | | | | | | | | | | | | | | | | | | | | | | Implement the RFC 5691 mitigation against Blind Reset attack using RST bit. Idea is to validate incoming RST sequence, to match RCV.NXT value, instead of previouly accepted window : (RCV.NXT <= SEG.SEQ < RCV.NXT+RCV.WND) If sequence is in window but not an exact match, send a "challenge ACK", so that the other part can resend an RST with the appropriate sequence. Add a new sysctl, tcp_challenge_ack_limit, to limit number of challenge ACK sent per second. Add a new SNMP counter to count number of challenge acks sent. (netstat -s | grep TCPChallengeACK) Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Kiran Kumar Kella <kkiran@broadcom.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: TCP Small QueuesEric Dumazet2012-07-121-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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 <edumazet@google.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Tom Herbert <therbert@google.com> Cc: Matt Mathis <mattmathis@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Nandita Dukkipati <nanditad@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Move timestamps from inetpeer to metrics cache.David S. Miller2012-07-111-1/+4
| | | | | | With help from Lin Ming. Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Maintain dynamic metrics in local cache.David S. Miller2012-07-111-0/+1
| | | | | | | | | | | | | | | | | | Maintain a local hash table of TCP dynamic metrics blobs. Computed TCP metrics are no longer maintained in the route metrics. The table uses RCU and an extremely simple hash so that it has low latency and low overhead. A simple hash is legitimate because we only make metrics blobs for fully established connections. Some tweaking of the default hash table sizes, metric timeouts, and the hash chain length limit certainly could use some tweaking. But the basic design seems sound. With help from Eric Dumazet and Joe Perches. Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Abstract back handling peer aliveness test into helper function.David S. Miller2012-07-111-0/+1
| | | | Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Move dynamnic metrics handling into seperate file.David S. Miller2012-07-111-0/+4
| | | | Signed-off-by: David S. Miller <davem@davemloft.net>
* ipv4: Kill early demux method return value.David S. Miller2012-06-281-1/+1
| | | | | | It's completely unnecessary. Signed-off-by: David S. Miller <davem@davemloft.net>
* Revert "ipv4: tcp: dont cache unconfirmed intput dst"David S. Miller2012-06-281-1/+1
| | | | | | | | | | | | | | This reverts commit c074da2810c118b3812f32d6754bd9ead2f169e7. This change has several unwanted side effects: 1) Sockets will cache the DST_NOCACHE route in sk->sk_rx_dst and we'll thus never create a real cached route. 2) All TCP traffic will use DST_NOCACHE and never use the routing cache at all. Signed-off-by: David S. Miller <davem@davemloft.net>
* ipv4: tcp: dont cache unconfirmed intput dstEric Dumazet2012-06-281-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | DDOS synflood attacks hit badly IP route cache. On typical machines, this cache is allowed to hold up to 8 Millions dst entries, 256 bytes for each, for a total of 2GB of memory. rt_garbage_collect() triggers and tries to cleanup things. Eventually route cache is disabled but machine is under fire and might OOM and crash. This patch exploits the new TCP early demux, to set a nocache boolean in case incoming TCP frame is for a not yet ESTABLISHED or TIMEWAIT socket. This 'nocache' boolean is then used in case dst entry is not found in route cache, to create an unhashed dst entry (DST_NOCACHE) SYN-cookie-ACK sent use a similar mechanism (ipv4: tcp: dont cache output dst for syncookies), so after this patch, a machine is able to absorb a DDOS synflood attack without polluting its IP route cache. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Hans Schillstrom <hans.schillstrom@ericsson.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* ipv4: Early TCP socket demux.David S. Miller2012-06-201-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Input packet processing for local sockets involves two major demuxes. One for the route and one for the socket. But we can optimize this down to one demux for certain kinds of local sockets. Currently we only do this for established TCP sockets, but it could at least in theory be expanded to other kinds of connections. If a TCP socket is established then it's identity is fully specified. This means that whatever input route was used during the three-way handshake must work equally well for the rest of the connection since the keys will not change. Once we move to established state, we cache the receive packet's input route to use later. Like the existing cached route in sk->sk_dst_cache used for output packets, we have to check for route invalidations using dst->obsolete and dst->ops->check(). Early demux occurs outside of a socket locked section, so when a route invalidation occurs we defer the fixup of sk->sk_rx_dst until we are actually inside of established state packet processing and thus have the socket locked. Signed-off-by: David S. Miller <davem@davemloft.net>
* [PATCH] tcp: Cache inetpeer in timewait socket, and only when necessary.David S. Miller2012-06-091-1/+0
| | | | | | | | | | | 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 <davem@davemloft.net>
* tcp: Get rid of inetpeer special cases.David S. Miller2012-06-091-1/+1
| | | | | | | | | | | | | | | | | | | The get_peer method TCP uses is full of special cases that make no sense accommodating, and it also gets in the way of doing more reasonable things here. First of all, if the socket doesn't have a usable cached route, there is no sense in trying to optimize timewait recycling. Likewise for the case where we have IP options, such as SRR enabled, that make the IP header destination address (and thus the destination address of the route key) differ from that of the connection's destination address. Just return a NULL peer in these cases, and thus we're also able to get rid of the clumsy inetpeer release logic. Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: bool conversionsEric Dumazet2012-05-171-28/+28
| | | | | | | | | | | bool conversions where possible. __inline__ -> inline space cleanups Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: Move rcvq sending to tcp_input.cPavel Emelyanov2012-05-111-2/+1
| | | | | | | | | It actually works on the input queue and will use its read mem routines, thus it's better to have in in the tcp_input.c file. Signed-off-by: Pavel Emelyanov <xemul@parallels.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: be more strict before accepting ECN negociationEric Dumazet2012-05-041-7/+16
| | | | | | | | | | | | | | | | | | | | | | It appears some networks play bad games with the two bits reserved for ECN. This can trigger false congestion notifications and very slow transferts. Since RFC 3168 (6.1.1) forbids SYN packets to carry CT bits, we can disable TCP ECN negociation if it happens we receive mangled CT bits in the SYN packet. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Perry Lorier <perryl@google.com> Cc: Matt Mathis <mattmathis@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Wilmer van der Gaast <wilmer@google.com> Cc: Ankur Jain <jankur@google.com> Cc: Tom Herbert <therbert@google.com> Cc: Dave Täht <dave.taht@bufferbloat.net> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net: implement tcp coalescing in tcp_queue_rcv()Eric Dumazet2012-05-031-1/+2
| | | | | | | | | | | | | | | | | Extend tcp coalescing implementing it from tcp_queue_rcv(), the main receiver function when application is not blocked in recvmsg(). Function tcp_queue_rcv() is moved a bit to allow its call from tcp_data_queue() This gives good results especially if GRO could not kick, and if skb head is a fragment. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Alexander Duyck <alexander.h.duyck@intel.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Tom Herbert <therbert@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: early retransmit: delayed fast retransmitYuchung Cheng2012-05-031-0/+3
| | | | | | | | | | | | | 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 <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* tcp: early retransmitYuchung Cheng2012-05-031-0/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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. http://conferences.sigcomm.org/imc/2011/docs/p155.pdf 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 <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* ipv6: RTAX_FEATURE_ALLFRAG causes inefficient TCP segment sizingEric Dumazet2012-04-271-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Quoting Tore Anderson from : https://bugzilla.kernel.org/show_bug.cgi?id=42572 When RTAX_FEATURE_ALLFRAG is set on a route, the effective TCP segment size does not take into account the size of the IPv6 Fragmentation header that needs to be included in outbound packets, causing every transmitted TCP segment to be fragmented across two IPv6 packets, the latter of which will only contain 8 bytes of actual payload. RTAX_FEATURE_ALLFRAG is typically set on a route in response to receving a ICMPv6 Packet Too Big message indicating a Path MTU of less than 1280 bytes. 1280 bytes is the minimum IPv6 MTU, however ICMPv6 PTBs with MTU < 1280 are still valid, in particular when an IPv6 packet is sent to an IPv4 destination through a stateless translator. Any ICMPv4 Need To Fragment packets originated from the IPv4 part of the path will be translated to ICMPv6 PTB which may then indicate an MTU of less than 1280. The Linux kernel refuses to reduce the effective MTU to anything below 1280 bytes, instead it sets it to exactly 1280 bytes, and RTAX_FEATURE_ALLFRAG is also set. However, the TCP segment size appears to be set to 1240 bytes (1280 Path MTU - 40 bytes of IPv6 header), instead of 1232 (additionally taking into account the 8 bytes required by the IPv6 Fragmentation extension header). This in turn results in rather inefficient transmission, as every transmitted TCP segment now is split in two fragments containing 1232+8 bytes of payload. After this patch, all the outgoing packets that includes a Fragmentation header all are "atomic" or "non-fragmented" fragments, i.e., they both have Offset=0 and More Fragments=0. With help from David S. Miller Reported-by: Tore Anderson <tore@fud.no> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Maciej Żenczykowski <maze@google.com> Cc: Tom Herbert <therbert@google.com> Tested-by: Tore Anderson <tore@fud.no> Signed-off-by: David S. Miller <davem@davemloft.net>
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