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path: root/net/ipv4/tcp_input.c
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2014-08-14tcp: fix ssthresh and undo for consecutive short FRTO episodesNeal Cardwell
Fix TCP FRTO logic so that it always notices when snd_una advances, indicating that any RTO after that point will be a new and distinct loss episode. Previously there was a very specific sequence that could cause FRTO to fail to notice a new loss episode had started: (1) RTO timer fires, enter FRTO and retransmit packet 1 in write queue (2) receiver ACKs packet 1 (3) FRTO sends 2 more packets (4) RTO timer fires again (should start a new loss episode) The problem was in step (3) above, where tcp_process_loss() returned early (in the spot marked "Step 2.b"), so that it never got to the logic to clear icsk_retransmits. Thus icsk_retransmits stayed non-zero. Thus in step (4) tcp_enter_loss() would see the non-zero icsk_retransmits, decide that this RTO is not a new episode, and decide not to cut ssthresh and remember the current cwnd and ssthresh for undo. There were two main consequences to the bug that we have observed. First, ssthresh was not decreased in step (4). Second, when there was a series of such FRTO (1-4) sequences that happened to be followed by an FRTO undo, we would restore the cwnd and ssthresh from before the entire series started (instead of the cwnd and ssthresh from before the most recent RTO). This could result in cwnd and ssthresh being restored to values much bigger than the proper values. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Fixes: e33099f96d99c ("tcp: implement RFC5682 F-RTO") Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-14tcp: don't allow syn packets without timestamps to pass tcp_tw_recycle logicHannes Frederic Sowa
tcp_tw_recycle heavily relies on tcp timestamps to build a per-host ordering of incoming connections and teardowns without the need to hold state on a specific quadruple for TCP_TIMEWAIT_LEN, but only for the last measured RTO. To do so, we keep the last seen timestamp in a per-host indexed data structure and verify if the incoming timestamp in a connection request is strictly greater than the saved one during last connection teardown. Thus we can verify later on that no old data packets will be accepted by the new connection. During moving a socket to time-wait state we already verify if timestamps where seen on a connection. Only if that was the case we let the time-wait socket expire after the RTO, otherwise normal TCP_TIMEWAIT_LEN will be used. But we don't verify this on incoming SYN packets. If a connection teardown was less than TCP_PAWS_MSL seconds in the past we cannot guarantee to not accept data packets from an old connection if no timestamps are present. We should drop this SYN packet. This patch closes this loophole. Please note, this patch does not make tcp_tw_recycle in any way more usable but only adds another safety check: Sporadic drops of SYN packets because of reordering in the network or in the socket backlog queues can happen. Users behing NAT trying to connect to a tcp_tw_recycle enabled server can get caught in blackholes and their connection requests may regullary get dropped because hosts behind an address translator don't have synchronized tcp timestamp clocks. tcp_tw_recycle cannot work if peers don't have tcp timestamps enabled. In general, use of tcp_tw_recycle is disadvised. Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Florian Westphal <fw@strlen.de> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-13net-timestamp: fix missing ACK timestampWillem de Bruijn
ACK timestamps are generated in tcp_clean_rtx_queue. The TSO datapath can break out early, causing the timestamp code to be skipped. Move the code up before the break. Reported-by: David S. Miller <davem@davemloft.net> Also fix a boundary condition: tp->snd_una is the next unacknowledged byte and between tests inclusive (a <= b <= c), so generate a an ACK timestamp if (prior_snd_una <= tskey <= tp->snd_una - 1). Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-05net-timestamp: ACK timestamp for bytestreamsWillem de Bruijn
Add SOF_TIMESTAMPING_TX_ACK, a request for a tstamp when the last byte in the send() call is acknowledged. It implements the feature for TCP. The timestamp is generated when the TCP socket cumulative ACK is moved beyond the tracked seqno for the first time. The feature ignores SACK and FACK, because those acknowledge the specific byte, but not necessarily the entire contents of the buffer up to that byte. Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-05tcp: reduce spurious retransmits due to transient SACK renegingNeal Cardwell
This commit reduces spurious retransmits due to apparent SACK reneging by only reacting to SACK reneging that persists for a short delay. When a sequence space hole at snd_una is filled, some TCP receivers send a series of ACKs as they apparently scan their out-of-order queue and cumulatively ACK all the packets that have now been consecutiveyly received. This is essentially misbehavior B in "Misbehaviors in TCP SACK generation" ACM SIGCOMM Computer Communication Review, April 2011, so we suspect that this is from several common OSes (Windows 2000, Windows Server 2003, Windows XP). However, this issue has also been seen in other cases, e.g. the netdev thread "TCP being hoodwinked into spurious retransmissions by lack of timestamps?" from March 2014, where the receiver was thought to be a BSD box. Since snd_una would temporarily be adjacent to a previously SACKed range in these scenarios, this receiver behavior triggered the Linux SACK reneging code path in the sender. This led the sender to clear the SACK scoreboard, enter CA_Loss, and spuriously retransmit (potentially) every packet from the entire write queue at line rate just a few milliseconds before the ACK for each packet arrives at the sender. To avoid such situations, now when a sender sees apparent reneging it does not yet retransmit, but rather adjusts the RTO timer to give the receiver a little time (max(RTT/2, 10ms)) to send us some more ACKs that will restore sanity to the SACK scoreboard. If the reneging persists until this RTO then, as before, we clear the SACK scoreboard and enter CA_Loss. A 10ms delay tolerates a receiver sending such a stream of ACKs at 56Kbit/sec. And to allow for receivers with slower or more congested paths, we wait for at least RTT/2. We validated the resulting max(RTT/2, 10ms) delay formula with a mix of North American and South American Google web server traffic, and found that for ACKs displaying transient reneging: (1) 90% of inter-ACK delays were less than 10ms (2) 99% of inter-ACK delays were less than RTT/2 In tests on Google web servers this commit reduced reneging events by 75%-90% (as measured by the TcpExtTCPSACKReneging counter), without any measurable impact on latency for user HTTP and SPDY requests. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-16Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-15tcp: Remove unnecessary arg from tcp_enter_cwr and tcp_init_cwnd_reductionChristoph Paasch
Since Yuchung's 9b44190dc11 (tcp: refactor F-RTO), tcp_enter_cwr is always called with set_ssthresh = 1. Thus, we can remove this argument from tcp_enter_cwr. Further, as we remove this one, tcp_init_cwnd_reduction is then always called with set_ssthresh = true, and so we can get rid of this argument as well. Cc: Yuchung Cheng <ycheng@google.com> Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-07tcp: fix false undo corner casesYuchung Cheng
The undo code assumes that, upon entering loss recovery, TCP 1) always retransmit something 2) the retransmission never fails locally (e.g., qdisc drop) so undo_marker is set in tcp_enter_recovery() and undo_retrans is incremented only when tcp_retransmit_skb() is successful. When the assumption is broken because TCP's cwnd is too small to retransmit or the retransmit fails locally. The next (DUP)ACK would incorrectly revert the cwnd and the congestion state in tcp_try_undo_dsack() or tcp_may_undo(). Subsequent (DUP)ACKs may enter the recovery state. The sender repeatedly enter and (incorrectly) exit recovery states if the retransmits continue to fail locally while receiving (DUP)ACKs. The fix is to initialize undo_retrans to -1 and start counting on the first retransmission. Always increment undo_retrans even if the retransmissions fail locally because they couldn't cause DSACKs to undo the cwnd reduction. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-29tcp: tcp_conn_request: fix build error when IPv6 is disabledOctavian Purdila
Fixes build error introduced by commit 1fb6f159fd21c64 (tcp: add tcp_conn_request): net/ipv4/tcp_input.c: In function 'pr_drop_req': net/ipv4/tcp_input.c:5889:130: error: 'struct sock_common' has no member named 'skc_v6_daddr' Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Octavian Purdila <octavian.purdila@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-27tcp: add tcp_conn_requestOctavian Purdila
Create tcp_conn_request and remove most of the code from tcp_v4_conn_request and tcp_v6_conn_request. Signed-off-by: Octavian Purdila <octavian.purdila@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-19tcp: fix tcp_match_skb_to_sack() for unaligned SACK at end of an skbNeal Cardwell
If there is an MSS change (or misbehaving receiver) that causes a SACK to arrive that covers the end of an skb but is less than one MSS, then tcp_match_skb_to_sack() was rounding up pkt_len to the full length of the skb ("Round if necessary..."), then chopping all bytes off the skb and creating a zero-byte skb in the write queue. This was visible now because the recently simplified TLP logic in bef1909ee3ed1c ("tcp: fixing TLP's FIN recovery") could find that 0-byte skb at the end of the write queue, and now that we do not check that skb's length we could send it as a TLP probe. Consider the following example scenario: mss: 1000 skb: seq: 0 end_seq: 4000 len: 4000 SACK: start_seq: 3999 end_seq: 4000 The tcp_match_skb_to_sack() code will compute: in_sack = false pkt_len = start_seq - TCP_SKB_CB(skb)->seq = 3999 - 0 = 3999 new_len = (pkt_len / mss) * mss = (3999/1000)*1000 = 3000 new_len += mss = 4000 Previously we would find the new_len > skb->len check failing, so we would fall through and set pkt_len = new_len = 4000 and chop off pkt_len of 4000 from the 4000-byte skb, leaving a 0-byte segment afterward in the write queue. With this new commit, we notice that the new new_len >= skb->len check succeeds, so that we return without trying to fragment. Fixes: adb92db857ee ("tcp: Make SACK code to split only at mss boundaries") Reported-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Ilpo Jarvinen <ilpo.jarvinen@helsinki.fi> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-10tcp: add gfp parameter to tcp_fragmentOctavian Purdila
tcp_fragment can be called from process context (from tso_fragment). Add a new gfp parameter to allow it to preserve atomic memory if possible. Signed-off-by: Octavian Purdila <octavian.purdila@intel.com> Reviewed-by: Christoph Paasch <christoph.paasch@uclouvain.be> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-03Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: include/net/inetpeer.h net/ipv6/output_core.c Changes in net were fixing bugs in code removed in net-next. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-02tcp: fix cwnd undo on DSACK in F-RTOYuchung Cheng
This bug is discovered by an recent F-RTO issue on tcpm list https://www.ietf.org/mail-archive/web/tcpm/current/msg08794.html The bug is that currently F-RTO does not use DSACK to undo cwnd in certain cases: upon receiving an ACK after the RTO retransmission in F-RTO, and the ACK has DSACK indicating the retransmission is spurious, the sender only calls tcp_try_undo_loss() if some never retransmisted data is sacked (FLAG_ORIG_DATA_SACKED). The correct behavior is to unconditionally call tcp_try_undo_loss so the DSACK information is used properly to undo the cwnd reduction. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-03tcp: remove in_flight parameter from cong_avoid() methodsEric Dumazet
Commit e114a710aa505 ("tcp: fix cwnd limited checking to improve congestion control") obsoleted in_flight parameter from tcp_is_cwnd_limited() and its callers. This patch does the removal as promised. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-20tcp: make tcp_cwnd_application_limited() staticWeiping Pan
Make tcp_cwnd_application_limited() static and move it from tcp_input.c to tcp_output.c Signed-off-by: Weiping Pan <wpan@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-11net: Fix use after free by removing length arg from sk_data_ready callbacks.David S. Miller
Several spots in the kernel perform a sequence like: skb_queue_tail(&sk->s_receive_queue, skb); sk->sk_data_ready(sk, skb->len); But at the moment we place the SKB onto the socket receive queue it can be consumed and freed up. So this skb->len access is potentially to freed up memory. Furthermore, the skb->len can be modified by the consumer so it is possible that the value isn't accurate. And finally, no actual implementation of this callback actually uses the length argument. And since nobody actually cared about it's value, lots of call sites pass arbitrary values in such as '0' and even '1'. So just remove the length argument from the callback, that way there is no confusion whatsoever and all of these use-after-free cases get fixed as a side effect. Based upon a patch by Eric Dumazet and his suggestion to audit this issue tree-wide. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-03-10tcp: timestamp SYN+DATA messagesEric Dumazet
All skb in socket write queue should be properly timestamped. In case of FastOpen, we special case the SYN+DATA 'message' as we queue in socket wrote queue the two fallback skbs: 1) SYN message by itself. 2) DATA segment by itself. We should make sure these skbs have proper timestamps. Add a WARN_ON_ONCE() to eventually catch future violations. Fixes: 740b0f1841f6 ("tcp: switch rtt estimations to usec resolution") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@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>
2014-03-05Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: drivers/net/wireless/ath/ath9k/recv.c drivers/net/wireless/mwifiex/pcie.c net/ipv6/sit.c The SIT driver conflict consists of a bug fix being done by hand in 'net' (missing u64_stats_init()) whilst in 'net-next' a helper was created (netdev_alloc_pcpu_stats()) which takes care of this. The two wireless conflicts were overlapping changes. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-03-03tcp: snmp stats for Fast Open, SYN rtx, and data pktsYuchung Cheng
Add the following snmp stats: TCPFastOpenActiveFail: Fast Open attempts (SYN/data) failed beacuse the remote does not accept it or the attempts timed out. TCPSynRetrans: number of SYN and SYN/ACK retransmits to break down retransmissions into SYN, fast-retransmits, timeout retransmits, etc. TCPOrigDataSent: number of outgoing packets with original data (excluding retransmission but including data-in-SYN). This counter is different from TcpOutSegs because TcpOutSegs also tracks pure ACKs. TCPOrigDataSent is more useful to track the TCP retransmission rate. Change TCPFastOpenActive to track only successful Fast Opens to be symmetric to TCPFastOpenPassive. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Nandita Dukkipati <nanditad@google.com> Signed-off-by: Lawrence Brakmo <brakmo@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-03-03tcp: fix bogus RTT on special retransmissionYuchung Cheng
RTT may be bogus with tall loss probe (TLP) when a packet is retransmitted and latter (s)acked without TCPCB_SACKED_RETRANS flag. For example, TLP calls __tcp_retransmit_skb() instead of tcp_retransmit_skb(). The skb timestamps are updated but the sacked flag is not marked with TCPCB_SACKED_RETRANS. As a result we'll get bogus RTT in tcp_clean_rtx_queue() or in tcp_sacktag_one() on spurious retransmission. The fix is to apply the sticky flag TCP_EVER_RETRANS to enforce Karn's check on RTT sampling. However this will disable F-RTO if timeout occurs after TLP, by resetting undo_marker in tcp_enter_loss(). We relax this check to only if any pending retransmists are still in-flight. 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>
2014-02-26tcp: switch rtt estimations to usec resolutionEric Dumazet
Upcoming congestion controls for TCP require usec resolution for RTT estimations. Millisecond resolution is simply not enough these days. FQ/pacing in DC environments also require this change for finer control and removal of bimodal behavior due to the current hack in tcp_update_pacing_rate() for 'small rtt' TCP_CONG_RTT_STAMP is no longer needed. As Julian Anastasov pointed out, we need to keep user compatibility : tcp_metrics used to export RTT and RTTVAR in msec resolution, so we added RTT_US and RTTVAR_US. An iproute2 patch is needed to use the new attributes if provided by the kernel. In this example ss command displays a srtt of 32 usecs (10Gbit link) lpk51:~# ./ss -i dst lpk52 Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port tcp ESTAB 0 1 10.246.11.51:42959 10.246.11.52:64614 cubic wscale:6,6 rto:201 rtt:0.032/0.001 ato:40 mss:1448 cwnd:10 send 3620.0Mbps pacing_rate 7240.0Mbps unacked:1 rcv_rtt:993 rcv_space:29559 Updated iproute2 ip command displays : lpk51:~# ./ip tcp_metrics | grep 10.246.11.52 10.246.11.52 age 561.914sec cwnd 10 rtt 274us rttvar 213us source 10.246.11.51 Old binary displays : lpk51:~# ip tcp_metrics | grep 10.246.11.52 10.246.11.52 age 561.914sec cwnd 10 rtt 250us rttvar 125us source 10.246.11.51 With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Yuchung Cheng <ycheng@google.com> Cc: Larry Brakmo <brakmo@google.com> Cc: Julian Anastasov <ja@ssi.bg> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-02-06tcp: remove 1ms offset in srtt computationEric Dumazet
TCP pacing depends on an accurate srtt estimation. Current srtt estimation is using jiffie resolution, and has an artificial offset of at least 1 ms, which can produce slowdowns when FQ/pacing is used, especially in DC world, where typical rtt is below 1 ms. We are planning a switch to usec resolution for linux-3.15, but in the meantime, this patch removes the 1 ms offset. All we need is to have tp->srtt minimal value of 1 to differentiate the case of srtt being initialized or not, not 8. The problematic behavior was observed on a 40Gbit testbed, where 32 concurrent netperf were reaching 12Gbps of aggregate speed, instead of line speed. This patch also has the effect of reporting more accurate srtt and send rates to iproute2 ss command as in : $ ss -i dst cca2 Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port tcp ESTAB 0 0 10.244.129.1:56984 10.244.129.2:12865 cubic wscale:6,6 rto:200 rtt:0.25/0.25 ato:40 mss:1448 cwnd:10 send 463.4Mbps rcv_rtt:1 rcv_space:29200 tcp ESTAB 0 390960 10.244.129.1:60247 10.244.129.2:50204 cubic wscale:6,6 rto:200 rtt:0.875/0.75 mss:1448 cwnd:73 ssthresh:51 send 966.4Mbps unacked:73 retrans:0/121 rcv_space:29200 Reported-by: Vytautas Valancius <valas@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-12-29tcp: make local functions staticstephen hemminger
The following are only used in one file: tcp_connect_init tcp_set_rto Signed-off-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-12-26ipv4: do clean up with spacesWeilong Chen
Fix checkpatch errors like: ERROR: spaces required around that XXX Signed-off-by: Weilong Chen <chenweilong@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-11-04tcp: properly handle stretch acks in slow startYuchung Cheng
Slow start now increases cwnd by 1 if an ACK acknowledges some packets, regardless the number of packets. Consequently slow start performance is highly dependent on the degree of the stretch ACKs caused by receiver or network ACK compression mechanisms (e.g., delayed-ACK, GRO, etc). But slow start algorithm is to send twice the amount of packets of packets left so it should process a stretch ACK of degree N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A follow up patch will use the remainder of the N (if greater than 1) to adjust cwnd in the congestion avoidance phase. In addition this patch retires the experimental limited slow start (LSS) feature. LSS has multiple drawbacks but questionable benefit. The fractional cwnd increase in LSS requires a loop in slow start even though it's rarely used. Configuring such an increase step via a global sysctl on different BDPS seems hard. Finally and most importantly the slow start overshoot concern is now better covered by the Hybrid slow start (hystart) enabled by default. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-11-04Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: drivers/net/ethernet/emulex/benet/be.h drivers/net/netconsole.c net/bridge/br_private.h Three mostly trivial conflicts. The net/bridge/br_private.h conflict was a function signature (argument addition) change overlapping with the extern removals from Joe Perches. In drivers/net/netconsole.c we had one change adjusting a printk message whilst another changed "printk(KERN_INFO" into "pr_info(". Lastly, the emulex change was a new inline function addition overlapping with Joe Perches's extern removals. Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-27tcp: do not rearm RTO when future data are sackedYuchung Cheng
Patch ed08495c3 "tcp: use RTT from SACK for RTO" always re-arms RTO upon obtaining a RTT sample from newly sacked data. But technically RTO should only be re-armed when the data sent before the last (re)transmission of write queue head are (s)acked. Otherwise the RTO may continue to extend during loss recovery on data sent in the future. Note that RTTs from ACK or timestamps do not have this problem, as the RTT source must be from data sent before. The new RTO re-arm policy is 1) Always re-arm RTO if SND.UNA is advanced 2) Re-arm RTO if sack RTT is available, provided the sacked data was sent before the last time write_queue_head was sent. Signed-off-by: Larry Brakmo <brakmo@google.com> 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>
2013-10-27tcp: only take RTT from timestamps if new data is ackedYuchung Cheng
Patch ed08495c3 "tcp: use RTT from SACK for RTO" has a bug that it does not check if the ACK acknowledge new data before taking the RTT sample from TCP timestamps. This patch adds the check back as required by the RFC. 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>
2013-10-27tcp: fix SYNACK RTT estimation in Fast OpenYuchung Cheng
tp->lsndtime may not always be the SYNACK timestamp if a passive Fast Open socket sends data before handshake completes. And if the remote acknowledges both the data and the SYNACK, the RTT sample is already taken in tcp_ack(), so no need to call tcp_update_ack_rtt() in tcp_synack_rtt_meas() aagain. 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>
2013-10-23Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: drivers/net/usb/qmi_wwan.c include/net/dst.h Trivial merge conflicts, both were overlapping changes. Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-21tcp: initialize passive-side sk_pacing_rate after 3WHSNeal Cardwell
For passive TCP connections, upon receiving the ACK that completes the 3WHS, make sure we set our pacing rate after we get our first RTT sample. On passive TCP connections, when we receive the ACK completing the 3WHS we do not take an RTT sample in tcp_ack(), but rather in tcp_synack_rtt_meas(). So upon receiving the ACK that completes the 3WHS, tcp_ack() leaves sk_pacing_rate at its initial value. Originally the initial sk_pacing_rate value was 0, so passive-side connections defaulted to sysctl_tcp_min_tso_segs (2 segs) in skbuffs made in the first RTT. With a default initial cwnd of 10 packets, this happened to be correct for RTTs 5ms or bigger, so it was hard to see problems in WAN or emulated WAN testing. Since 7eec4174ff ("pkt_sched: fq: fix non TCP flows pacing"), the initial sk_pacing_rate is 0xffffffff. So after that change, passive TCP connections were keeping this value (and using large numbers of segments per skbuff) until receiving an ACK for data. Signed-off-by: Neal Cardwell <ncardwell@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-17tcp: fix incorrect ca_state in tail loss probeYuchung Cheng
On receiving an ACK that covers the loss probe sequence, TLP immediately sets the congestion state to Open, even though some packets are not recovered and retransmisssion are on the way. The later ACks may trigger a WARN_ON check in step D of tcp_fastretrans_alert(), e.g., https://bugzilla.redhat.com/show_bug.cgi?id=989251 The fix is to follow the similar procedure in recovery by calling tcp_try_keep_open(). The sender switches to Open state if no packets are retransmissted. Otherwise it goes to Disorder and let subsequent ACKs move the state to Recovery or Open. Reported-By: Michael Sterrett <michael@sterretts.net> Tested-By: Dormando <dormando@rydia.net> Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-10tcp: use ACCESS_ONCE() in tcp_update_pacing_rate()Eric Dumazet
sk_pacing_rate is read by sch_fq packet scheduler at any time, with no synchronization, so make sure we update it in a sensible way. ACCESS_ONCE() is how we instruct compiler to not do stupid things, like using the memory location as a temporary variable. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-08Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: include/linux/netdevice.h net/core/sock.c Trivial merge issues. Removal of "extern" for functions declaration in netdevice.h at the same time "const" was added to an argument. Two parallel line additions in net/core/sock.c Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-04tcp: do not forget FIN in tcp_shifted_skb()Eric Dumazet
Yuchung found following problem : There are bugs in the SACK processing code, merging part in tcp_shift_skb_data(), that incorrectly resets or ignores the sacked skbs FIN flag. When a receiver first SACK the FIN sequence, and later throw away ofo queue (e.g., sack-reneging), the sender will stop retransmitting the FIN flag, and hangs forever. Following packetdrill test can be used to reproduce the bug. $ cat sack-merge-bug.pkt `sysctl -q net.ipv4.tcp_fack=0` // Establish a connection and send 10 MSS. 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +.000 bind(3, ..., ...) = 0 +.000 listen(3, 1) = 0 +.050 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7> +.000 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6> +.001 < . 1:1(0) ack 1 win 1024 +.000 accept(3, ..., ...) = 4 +.100 write(4, ..., 12000) = 12000 +.000 shutdown(4, SHUT_WR) = 0 +.000 > . 1:10001(10000) ack 1 +.050 < . 1:1(0) ack 2001 win 257 +.000 > FP. 10001:12001(2000) ack 1 +.050 < . 1:1(0) ack 2001 win 257 <sack 10001:11001,nop,nop> +.050 < . 1:1(0) ack 2001 win 257 <sack 10001:12002,nop,nop> // SACK reneg +.050 < . 1:1(0) ack 12001 win 257 +0 %{ print "unacked: ",tcpi_unacked }% +5 %{ print "" }% First, a typo inverted left/right of one OR operation, then code forgot to advance end_seq if the merged skb carried FIN. Bug was added in 2.6.29 by commit 832d11c5cd076ab ("tcp: Try to restore large SKBs while SACK processing") Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-03net: ipv4: Change variable type to boolPeter Senna Tschudin
The variable fully_acked is only assigned the values true and false. Change its type to bool. The simplified semantic patch that find this problem is as follows (http://coccinelle.lip6.fr/): @exists@ type T; identifier b; @@ - T + bool b = ...; ... when any b = \(true\|false\) Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-02tcp: sndbuf autotuning improvementsEric Dumazet
tcp_fixup_sndbuf() is underestimating initial send buffer requirements. It was not noticed because big GSO packets were escaping the limitation, but with smaller TSO packets (or TSO/GSO/SG off), application hits sk_sndbuf before having a chance to fill enough packets in socket write queue. - initial cwnd can be bigger than 10 for specific routes - SKB_TRUESIZE() is a bit under real needs in some cases, because of power-of-two rounding in kmalloc() - Fast Recovery (RFC 5681 3.2) : Cubic needs 70% factor - Extra cushion (application might react slowly to POLLOUT) tcp_v4_conn_req_fastopen() needs to call tcp_init_metrics() before calling tcp_init_buffer_space() Then we realize tcp_new_space() should call tcp_fixup_sndbuf() instead of duplicating this stuff. Rename tcp_fixup_sndbuf() to tcp_sndbuf_expand() to be more descriptive. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Maciej Żenczykowski <maze@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-28net: introduce SO_MAX_PACING_RATEEric Dumazet
As mentioned in commit afe4fd062416b ("pkt_sched: fq: Fair Queue packet scheduler"), this patch adds a new socket option. SO_MAX_PACING_RATE offers the application the ability to cap the rate computed by transport layer. Value is in bytes per second. u32 val = 1000000; setsockopt(sockfd, SOL_SOCKET, SO_MAX_PACING_RATE, &val, sizeof(val)); To be effectively paced, a flow must use FQ packet scheduler. Note that a packet scheduler takes into account the headers for its computations. The effective payload rate depends on MSS and retransmits if any. I chose to make this pacing rate a SOL_SOCKET option instead of a TCP one because this can be used by other protocols. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Steinar H. Gunderson <sesse@google.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-24tcp: fix dynamic right sizingEric Dumazet
Dynamic Right Sizing (DRS) is supposed to open TCP receive window automatically, but suffers from two bugs, presented by order of importance. 1) tcp_rcv_space_adjust() fix : Using twice the last received amount is very pessimistic, because it doesn't allow fast recovery or proper slow start ramp up, if sender wants to increase cwin by 100% every RTT. copied = bytes received in previous RTT 2*copied = bytes we expect to receive in next RTT 4*copied = bytes we need to advertise in rwin at end of next RTT DRS is one RTT late, it needs a 4x factor. If sender is not using ABC, and increases cwin by 50% every rtt, then we needed 1.5*1.5 = 2.25 factor. This is probably why this bug was not really noticed. 2) There is no window adjustment after first RTT. DRS triggers only after the second RTT. DRS needs two RTT to initialize, so tcp_fixup_rcvbuf() should setup sk_rcvbuf to allow proper window grow for first two RTT. This patch increases TCP efficiency particularly for large RTT flows when autotuning is used at the receiver, and more particularly in presence of packet losses. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Cc: Van Jacobson <vanj@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-06tcp: properly increase rcv_ssthresh for ofo packetsEric Dumazet
TCP receive window handling is multi staged. A socket has a memory budget, static or dynamic, in sk_rcvbuf. Because we do not really know how this memory budget translates to a TCP window (payload), TCP announces a small initial window (about 20 MSS). When a packet is received, we increase TCP rcv_win depending on the payload/truesize ratio of this packet. Good citizen packets give a hint that it's reasonable to have rcv_win = sk_rcvbuf/2 This heuristic takes place in tcp_grow_window() Problem is : We currently call tcp_grow_window() only for in-order packets. This means that reorders or packet losses stop proper grow of rcv_win, and senders are unable to benefit from fast recovery, or proper reordering level detection. Really, a packet being stored in OFO queue is not a bad citizen. It should be part of the game as in-order packets. In our traces, we very often see sender is limited by linux small receive windows, even if linux hosts use autotuning (DRS) and should allow rcv_win to grow to ~3MB. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-06tcp: fix no cwnd growth after timeoutYuchung Cheng
In commit 0f7cc9a3 "tcp: increase throughput when reordering is high", it only allows cwnd to increase in Open state. This mistakenly disables slow start after timeout (CA_Loss). Moreover cwnd won't grow if the state moves from Disorder to Open later in tcp_fastretrans_alert(). Therefore the correct logic should be to allow cwnd to grow as long as the data is received in order in Open, Loss, or even Disorder state. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-05Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller
Conflicts: drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c net/bridge/br_multicast.c net/ipv6/sit.c The conflicts were minor: 1) sit.c changes overlap with change to ip_tunnel_xmit() signature. 2) br_multicast.c had an overlap between computing max_delay using msecs_to_jiffies and turning MLDV2_MRC() into an inline function with a name using lowercase instead of uppercase letters. 3) stmmac had two overlapping changes, one which conditionally allocated and hooked up a dma_cfg based upon the presence of the pbl OF property, and another one handling store-and-forward DMA made. The latter of which should not go into the new of_find_property() basic block. Signed-off-by: David S. Miller <davem@davemloft.net>
2013-09-04tcp: Change return value of tcp_rcv_established()Vijay Subramanian
tcp_rcv_established() returns only one value namely 0. We change the return value to void (as suggested by David Miller). After commit 0c24604b (tcp: implement RFC 5961 4.2), we no longer send RSTs in response to SYNs. We can remove the check and processing on the return value of tcp_rcv_established(). We also fix jtcp_rcv_established() in tcp_probe.c to match that of tcp_rcv_established(). Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-29tcp: TSO packets automatic sizingEric Dumazet
After hearing many people over past years complaining against TSO being bursty or even buggy, we are proud to present automatic sizing of TSO packets. One part of the problem is that tcp_tso_should_defer() uses an heuristic relying on upcoming ACKS instead of a timer, but more generally, having big TSO packets makes little sense for low rates, as it tends to create micro bursts on the network, and general consensus is to reduce the buffering amount. This patch introduces a per socket sk_pacing_rate, that approximates the current sending rate, and allows us to size the TSO packets so that we try to send one packet every ms. This field could be set by other transports. Patch has no impact for high speed flows, where having large TSO packets makes sense to reach line rate. For other flows, this helps better packet scheduling and ACK clocking. This patch increases performance of TCP flows in lossy environments. A new sysctl (tcp_min_tso_segs) is added, to specify the minimal size of a TSO packet (default being 2). A follow-up patch will provide a new packet scheduler (FQ), using sk_pacing_rate as an input to perform optional per flow pacing. This explains why we chose to set sk_pacing_rate to twice the current rate, allowing 'slow start' ramp up. sk_pacing_rate = 2 * cwnd * mss / srtt v2: Neal Cardwell reported a suspect deferring of last two segments on initial write of 10 MSS, I had to change tcp_tso_should_defer() to take into account tp->xmit_size_goal_segs Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Van Jacobson <vanj@google.com> Cc: Tom Herbert <therbert@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-29tcp: don't apply tsoffset if rcv_tsecr is zeroAndrew Vagin
The zero value means that tsecr is not valid, so it's a special case. tsoffset is used to customize tcp_time_stamp for one socket. tsoffset is usually zero, it's used when a socket was moved from one host to another host. Currently this issue affects logic of tcp_rcv_rtt_measure_ts. Due to incorrect value of rcv_tsecr, tcp_rcv_rtt_measure_ts sets rto to TCP_RTO_MAX. Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: "David S. Miller" <davem@davemloft.net> 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> Reported-by: Cyrill Gorcunov <gorcunov@openvz.org> Signed-off-by: Andrey Vagin <avagin@openvz.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-22tcp: increase throughput when reordering is highYuchung Cheng
The stack currently detects reordering and avoid spurious retransmission very well. However the throughput is sub-optimal under high reordering because cwnd is increased only if the data is deliverd in order. I.e., FLAG_DATA_ACKED check in tcp_ack(). The more packet are reordered the worse the throughput is. Therefore when reordering is proven high, cwnd should advance whenever the data is delivered regardless of its ordering. If reordering is low, conservatively advance cwnd only on ordered deliveries in Open state, and retain cwnd in Disordered state (RFC5681). Using netperf on a qdisc setup of 20Mbps BW and random RTT from 45ms to 55ms (for reordering effect). This change increases TCP throughput by 20 - 25% to near bottleneck BW. A special case is the stretched ACK with new SACK and/or ECE mark. For example, a receiver may receive an out of order or ECN packet with unacked data buffered because of LRO or delayed ACK. The principle on such an ACK is to advance cwnd on the cummulative acked part first, then reduce cwnd in tcp_fastretrans_alert(). 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>
2013-08-13tcp: reset reordering est. selectively on timeoutYuchung Cheng
On timeout the TCP sender unconditionally resets the estimated degree of network reordering (tp->reordering). The idea behind this is that the estimate is too large to trigger fast recovery (e.g., due to a IP path change). But for example if the sender only had 2 packets outstanding, then a timeout doesn't tell much about reordering. A sender that learns about reordering on big writes and loses packets on small writes will end up falsely retransmitting again and again, especially when reordering is more likely on big writes. Therefore the sender should only suspect that tp->reordering is too high if it could have gone into fast recovery with the (lower) default estimate. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-07-22tcp: use RTT from SACK for RTOYuchung Cheng
If RTT is not available because Karn's check has failed or no new packet is acked, use the RTT measured from SACK to estimate the RTO. The sender can continue to estimate the RTO during loss recovery or reordering event upon receiving non-partial ACKs. This also changes when the RTO is re-armed. Previously it is only re-armed when some data is cummulatively acknowledged (i.e., SND.UNA advances), but now it is re-armed whenever RTT estimator is updated. This feature is particularly useful to reduce spurious timeout for buffer bloat including cellular carriers [1], and RTT estimation on reordering events. [1] "An In-depth Study of LTE: Effect of Network Protocol and Application Behavior on Performance", In Proc. of SIGCOMM 2013 Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-07-22tcp: measure RTT from new SACKYuchung Cheng
Take RTT sample if an ACK selectively acks some sequences that have never been retransmitted. The Karn's algorithm does not apply even if that ACK (s)acks other retransmitted sequences, because it must been generated by an original but perhaps out-of-order packet. There is no ambiguity. In case when multiple blocks are newly sacked because of ACK losses the earliest block is used to measure RTT, similar to cummulative ACKs. Such RTT samples allow the sender to estimate the RTO during loss recovery and packet reordering events. It is still useful even with TCP timestamps. That's because during these events the SND.UNA may not advance preventing RTT samples from TS ECR (thus the FLAG_ACKED check before calling tcp_ack_update_rtt()). Therefore this new RTT source is complementary to existing ACK and TS RTT mechanisms. This patch does not update the RTO. It is done in the next patch. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>