BMC/Intel-BMC/linux.git/net/ipv4/tcp_output.c, branch dev

tcp: remove obsolete check in tcp_set_skb_tso_segs()

2015-06-11T23:33:11+00:00

We had various issues in the past when TCP stack was modifying gso_size/gso_segs while clones were in flight. Commit c52e2421f73 ("tcp: must unclone packets before mangling them") fixed these bugs and added a WARN_ON_ONCE(skb_cloned(skb)); in tcp_set_skb_tso_segs() These bugs are now fixed, and because TCP stack now only sets shinfo->gso_size|segs on the clone itself, the check can be removed. As a result of this change, compiler inlines tcp_set_skb_tso_segs() in tcp_init_tso_segs() Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: fill shinfo->gso_size at last moment

2015-06-11T23:33:11+00:00

In commit cd7d8498c9a5 ("tcp: change tcp_skb_pcount() location") we stored gso_segs in a temporary cache hot location. This patch does the same for gso_size. This allows to save 2 cache line misses in tcp xmit path for the last packet that is considered but not sent because of various conditions (cwnd, tso defer, receiver window, TSQ...) Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: tcp_set_skb_tso_segs() no longer need struct sock parameter

2015-06-11T23:33:11+00:00

tcp_set_skb_tso_segs() & tcp_init_tso_segs() no longer use the sock pointer. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: fill shinfo->gso_type at last moment

2015-06-11T23:33:11+00:00

Our goal is to touch skb_shinfo(skb) only when absolutely needed, to avoid two cache line misses in TCP output path for last skb that is considered but not sent because of various conditions (cwnd, tso defer, receiver window, TSQ...) A packet is GSO only when skb_shinfo(skb)->gso_size is not zero. We can set skb_shinfo(skb)->gso_type to sk->sk_gso_type even for non GSO packets. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: double default TSQ output bytes limit

2015-06-04T08:09:36+00:00

Xen virtual network driver has higher latency than a physical NIC. Having only 128K as limit for TSQ introduced 30% regression in guest throughput. This patch raises the limit to 256K. This reduces the regression to 8%. This buys us more time to work out a proper solution in the long run. Signed-off-by: Wei Liu Cc: David Miller Cc: Eric Dumazet Acked-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: tcp_tso_autosize() minimum is one packet

2015-05-27T03:21:29+00:00

By making sure sk->sk_gso_max_segs minimal value is one, and sysctl_tcp_min_tso_segs minimal value is one as well, tcp_tso_autosize() will return a non zero value. We can then revert 843925f33fcc293d80acf2c5c8a78adf3344d49b ("tcp: Do not apply TSO segment limit to non-TSO packets") and save few cpu cycles in fast path. Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Herbert Xu Acked-by: Neal Cardwell Acked-by: Herbert Xu Signed-off-by: David S. Miller

tcp: add tcpi_segs_in and tcpi_segs_out to tcp_info

2015-05-22T03:25:21+00:00

This patch tracks the total number of inbound and outbound segments on a TCP socket. One may use this number to have an idea on connection quality when compared against the retransmissions. RFC4898 named these : tcpEStatsPerfSegsIn and tcpEStatsPerfSegsOut These are a 32bit field each and can be fetched both from TCP_INFO getsockopt() if one has a handle on a TCP socket, or from inet_diag netlink facility (iproute2/ss patch will follow) Note that tp->segs_out was placed near tp->snd_nxt for good data locality and minimal performance impact, while tp->segs_in was placed near tp->bytes_received for the same reason. Join work with Eric Dumazet. Note that received SYN are accounted on the listener, but sent SYNACK are not accounted. Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: add a force_schedule argument to sk_stream_alloc_skb()

2015-05-21T20:56:40+00:00

In commit 8e4d980ac215 ("tcp: fix behavior for epoll edge trigger") we fixed a possible hang of TCP sockets under memory pressure, by allowing sk_stream_alloc_skb() to use sk_forced_mem_schedule() if no packet is in socket write queue. It turns out there are other cases where we want to force memory schedule : tcp_fragment() & tso_fragment() need to split a big TSO packet into two smaller ones. If we block here because of TCP memory pressure, we can effectively block TCP socket from sending new data. If no further ACK is coming, this hang would be definitive, and socket has no chance to effectively reduce its memory usage. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: add rfc3168, section 6.1.1.1. fallback

2015-05-19T20:53:37+00:00

This work as a follow-up of commit f7b3bec6f516 ("net: allow setting ecn via routing table") and adds RFC3168 section 6.1.1.1. fallback for outgoing ECN connections. In other words, this work adds a retry with a non-ECN setup SYN packet, as suggested from the RFC on the first timeout: [...] A host that receives no reply to an ECN-setup SYN within the normal SYN retransmission timeout interval MAY resend the SYN and any subsequent SYN retransmissions with CWR and ECE cleared. [...] Schematic client-side view when assuming the server is in tcp_ecn=2 mode, that is, Linux default since 2009 via commit 255cac91c3c9 ("tcp: extend ECN sysctl to allow server-side only ECN"): 1) Normal ECN-capable path: SYN ECE CWR -----> <----- SYN ACK ECE ACK -----> 2) Path with broken middlebox, when client has fallback: SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN -----> <----- SYN ACK ACK -----> In case we would not have the fallback implemented, the middlebox drop point would basically end up as: SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) In any case, it's rather a smaller percentage of sites where there would occur such additional setup latency: it was found in end of 2014 that ~56% of IPv4 and 65% of IPv6 servers of Alexa 1 million list would negotiate ECN (aka tcp_ecn=2 default), 0.42% of these webservers will fail to connect when trying to negotiate with ECN (tcp_ecn=1) due to timeouts, which the fallback would mitigate with a slight latency trade-off. Recent related paper on this topic: Brian Trammell, Mirja Kühlewind, Damiano Boppart, Iain Learmonth, Gorry Fairhurst, and Richard Scheffenegger: "Enabling Internet-Wide Deployment of Explicit Congestion Notification." Proc. PAM 2015, New York. http://ecn.ethz.ch/ecn-pam15.pdf Thus, when net.ipv4.tcp_ecn=1 is being set, the patch will perform RFC3168, section 6.1.1.1. fallback on timeout. For users explicitly not wanting this which can be in DC use case, we add a net.ipv4.tcp_ecn_fallback knob that allows for disabling the fallback. tp->ecn_flags are not being cleared in tcp_ecn_clear_syn() on output, but rather we let tcp_ecn_rcv_synack() take that over on input path in case a SYN ACK ECE was delayed. Thus a spurious SYN retransmission will not prevent ECN being negotiated eventually in that case. Reference: https://www.ietf.org/proceedings/92/slides/slides-92-iccrg-1.pdf Reference: https://www.ietf.org/proceedings/89/slides/slides-89-tsvarea-1.pdf Signed-off-by: Daniel Borkmann Signed-off-by: Florian Westphal Signed-off-by: Mirja Kühlewind Signed-off-by: Brian Trammell Cc: Eric Dumazet Cc: Dave That Acked-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: introduce tcp_under_memory_pressure()

2015-05-18T02:45:48+00:00

Introduce an optimized version of sk_under_memory_pressure() for TCP. Our intent is to use it in fast paths. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller