kernel/linux.git/include/net/tcp.h, branch v3.10.47

net-tcp: fastopen: fix high order allocations

2014-03-24T04:38:10+00:00

[ Upstream commit f5ddcbbb40aa0ba7fbfe22355d287603dbeeaaac ] This patch fixes two bugs in fastopen : 1) The tcp_sendmsg(..., @size) argument was ignored. Code was relying on user not fooling the kernel with iovec mismatches 2) When MTU is about 64KB, tcp_send_syn_data() attempts order-5 allocations, which are likely to fail when memory gets fragmented. Fixes: 783237e8daf13 ("net-tcp: Fast Open client - sending SYN-data") Signed-off-by: Eric Dumazet Cc: Yuchung Cheng Acked-by: Yuchung Cheng Tested-by: Yuchung Cheng Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

tcp: TSO packets automatic sizing

2013-11-04T12:30:59+00:00

[ Upstream commits 6d36824e730f247b602c90e8715a792003e3c5a7, 02cf4ebd82ff0ac7254b88e466820a290ed8289a, and parts of 7eec4174ff29cd42f2acfae8112f51c228545d40 ] 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 Cc: Neal Cardwell Cc: Yuchung Cheng Cc: Van Jacobson Cc: Tom Herbert Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

tcp: GSO should be TSQ friendly

2013-04-12T22:17:06+00:00

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 Cc: Tom Herbert Cc: Yuchung Cheng Cc: Nandita Dukkipati Cc: Neal Cardwell Signed-off-by: David S. Miller

tcp: Remove dead sysctl_tcp_cookie_size declaration

2013-04-02T18:26:50+00:00

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 Signed-off-by: David S. Miller

tcp: refactor F-RTO

2013-03-21T15:47:50+00:00

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 Acked-by: Neal Cardwell Acked-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: Remove TCPCT

2013-03-17T18:35:13+00:00

TCPCT uses option-number 253, reserved for experimental use and should not be used in production environments. Further, TCPCT does not fully implement RFC 6013. As a nice side-effect, removing TCPCT increases TCP's performance for very short flows: Doing an apache-benchmark with -c 100 -n 100000, sending HTTP-requests for files of 1KB size. before this patch: average (among 7 runs) of 20845.5 Requests/Second after: average (among 7 runs) of 21403.6 Requests/Second Signed-off-by: Christoph Paasch Signed-off-by: David S. Miller

tcp: Tail loss probe (TLP)

2013-03-12T12:30:34+00:00

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 Acked-by: Neal Cardwell Acked-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp: uninline tcp_prequeue()

2013-03-07T21:22:39+00:00

tcp_prequeue() became too big to be inlined. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: avoid wakeups for pure ACK

2013-02-28T20:37:29+00:00

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 Cc: Neal Cardwell Cc: Tom Herbert Cc: Yuchung Cheng Cc: Andi Kleen Signed-off-by: David S. Miller

tcp: remove Appropriate Byte Count support

2013-02-05T19:51:16+00:00

TCP Appropriate Byte Count was added by me, but later disabled. There is no point in maintaining it since it is a potential source of bugs and Linux already implements other better window protection heuristics. Signed-off-by: Stephen Hemminger Signed-off-by: David S. Miller