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46d3ceabd8
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> |
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| .. | ||
| datagram.c | ||
| dev_addr_lists.c | ||
| dev.c | ||
| drop_monitor.c | ||
| dst.c | ||
| ethtool.c | ||
| fib_rules.c | ||
| filter.c | ||
| flow_dissector.c | ||
| flow.c | ||
| gen_estimator.c | ||
| gen_stats.c | ||
| iovec.c | ||
| link_watch.c | ||
| Makefile | ||
| neighbour.c | ||
| net_namespace.c | ||
| net-sysfs.c | ||
| net-sysfs.h | ||
| net-traces.c | ||
| netevent.c | ||
| netpoll.c | ||
| netprio_cgroup.c | ||
| pktgen.c | ||
| request_sock.c | ||
| rtnetlink.c | ||
| scm.c | ||
| secure_seq.c | ||
| skbuff.c | ||
| sock_diag.c | ||
| sock.c | ||
| stream.c | ||
| sysctl_net_core.c | ||
| timestamping.c | ||
| user_dma.c | ||
| utils.c | ||