[mptcp-next,4/4] mptcp: use copy_from_iter helpers on transmit..

Commit Message

Paolo Abeni Sept. 20, 2023, 12:45 p.m. UTC

The perf traces show an high cost for the MPTCP transmit path memcpy.

It turn out that the helper currently in use carries quite a bit
of unneeded overhead, e.g. to map/unmap the memory pages.

Moving to the 'copy_from_iter' variant removes such overhead and
additionally gains the no-cache support.

Signed-off-by: Paolo Abeni <[e-mail]>
---
 net/mptcp/protocol.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

Patch

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 1de8eaccd48b..6f9e116598ed 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1766,6 +1766,18 @@  static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
 	return ret;
 }
 
+static int do_copy_data_nocache(struct sock *sk, int copy,
+				struct iov_iter *from, char *to)
+{
+	if (sk->sk_route_caps & NETIF_F_NOCACHE_COPY) {
+		if (!copy_from_iter_full_nocache(to, copy, from))
+			return -EFAULT;
+	} else if (!copy_from_iter_full(to, copy, from)) {
+		return -EFAULT;
+	}
+	return 0;
+}
+
 static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
@@ -1839,11 +1851,10 @@  static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (!sk_wmem_schedule(sk, total_ts))
 			goto wait_for_memory;
 
-		if (copy_page_from_iter(dfrag->page, offset, psize,
-					&msg->msg_iter) != psize) {
-			ret = -EFAULT;
+		ret = do_copy_data_nocache(sk, psize, &msg->msg_iter,
+					   page_address(dfrag->page) + offset);
+		if (ret)
 			goto do_error;
-		}
 
 		/* data successfully copied into the write queue */
 		sk_forward_alloc_add(sk, -total_ts);