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>
---
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