netdev - [PATCH net-next 6/9] mptcp: use copy_from

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Message-Id: <20231023-send-net-next-20231023-2-v1-6-9dc60939d371@kernel.org>
Date: Mon, 23 Oct 2023 13:44:39 -0700
From: Mat Martineau <martineau@...nel.org>
To: Matthieu Baerts <matttbe@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 Mat Martineau <martineau@...nel.org>
Subject: [PATCH net-next 6/9] mptcp: use copy_from_iter helpers on transmit

From: Paolo Abeni <pabeni@...hat.com>

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.

Reviewed-by: Mat Martineau <martineau@...nel.org>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Mat Martineau <martineau@...nel.org>
---
 net/mptcp/protocol.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 7036e30c449f..5489f024dd7e 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1760,6 +1760,18 @@ 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);
@@ -1833,11 +1845,10 @@ 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);

-- 
2.41.0