Currently the xmit path of the MPTCP protocol creates smaller- than-max-size skbs, which is suboptimal for the performances. There are a few things to improve: - when coalescing to an existing skb, must clear the PUSH flag - tcp_build_frag() expect the available space as an argument. When coalescing is enable MPTCP already subtracted the to-be-coalesced skb len. We must increment said argument accordingly. Before: ./use_mptcp.sh netperf -H 127.0.0.1 -t TCP_STREAM [...] 131072 16384 16384 30.00 24414.86 After: ./use_mptcp.sh netperf -H 127.0.0.1 -t TCP_STREAM [...] 131072 16384 16384 30.05 28357.69 Signed-off-by: Paolo Abeni <pabeni(a)redhat.com&gt; --- use_mptcp.sh forces exiting app to create MPTCP instead of TCP ones via LD_PRELOAD of crafter socket() implementation. https://github.com/pabeni/mptcp-tools/tree/master/use_mptcp --- v2 -> v3: - drop the tcp bits. They caused stream corruption which could not be easily set, and dropping them does not affect the performance in a visible way, since that code path is hit only on corner cases v1 -> v2: - prevent splitting if from_ext is frozen: should never happen but is cheap - provide dummy mptcp_skb_split() for non MPTCP build --- net/mptcp/protocol.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 2a8174a7e630..82525d454c5e 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1256,6 +1256,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk, struct mptcp_ext *mpext = NULL; struct sk_buff *skb, *tail; bool can_collapse = false; + int size_bias = 0; int avail_size; size_t ret = 0; @@ -1277,10 +1278,12 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk, mpext = skb_ext_find(skb, SKB_EXT_MPTCP); can_collapse = (info->size_goal - skb->len > 0) && mptcp_skb_can_collapse_to(data_seq, skb, mpext); - if (!can_collapse) + if (!can_collapse) { TCP_SKB_CB(skb)->eor = 1; - else + } else { + size_bias = skb->len; avail_size = info->size_goal - skb->len; + } } /* Zero window and all data acked? Probe. */ @@ -1300,8 +1303,8 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk, return 0; ret = info->limit - info->sent; - tail = tcp_build_frag(ssk, avail_size, info->flags, dfrag->page, - dfrag->offset + info->sent, &ret); + tail = tcp_build_frag(ssk, avail_size + size_bias, info->flags, + dfrag->page, dfrag->offset + info->sent, &ret); if (!tail) { tcp_remove_empty_skb(sk, tcp_write_queue_tail(ssk)); return -ENOMEM; @@ -1310,8 +1313,9 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk, /* if the tail skb is still the cached one, collapsing really happened. */ if (skb == tail) { - WARN_ON_ONCE(!can_collapse); + TCP_SKB_CB(tail)->tcp_flags &= ~TCPHDR_PSH; mpext->data_len += ret; + WARN_ON_ONCE(!can_collapse); WARN_ON_ONCE(zero_window_probe); goto out; } -- 2.26.2