Commit ad02c4f5 authored Jan 04, 2017 by Soheil Hassas Yeganeh Committed by David S. Miller Jan 05, 2017

tcp: provide timestamps for partial writes



For TCP sockets, TX timestamps are only captured when the user data
is successfully and fully written to the socket. In many cases,
however, TCP writes can be partial for which no timestamp is
collected.

Collect timestamps whenever any user data is (fully or partially)
copied into the socket. Pass tcp_write_queue_tail to tcp_tx_timestamp
instead of the local skb pointer since it can be set to NULL on
the error path.

Note that tcp_write_queue_tail can be NULL, even if bytes have been
copied to the socket. This is because acknowledgements are being
processed in tcp_sendmsg(), and by the time tcp_tx_timestamp is
called tcp_write_queue_tail can be NULL. For such cases, this patch
does not collect any timestamps (i.e., it is best-effort).

This patch is written with suggestions from Willem de Bruijn and
Eric Dumazet.

Change-log V1 -> V2:
	- Use sockc.tsflags instead of sk->sk_tsflags.
	- Use the same code path for normal writes and errors.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 37e65dc1

net/ipv4/tcp.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -429,7 +429,7 @@ EXPORT_SYMBOL(tcp_init_sock);

		static void tcp_tx_timestamp(struct sock sk, u16 tsflags, struct sk_buff skb)
		{
		if (tsflags) {
		if (tsflags && skb) {
		struct skb_shared_info *shinfo = skb_shinfo(skb);
		struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);

		@@ -958,10 +958,8 @@ new_segment:
		copied += copy;
		offset += copy;
		size -= copy;
		if (!size) {
		tcp_tx_timestamp(sk, sk->sk_tsflags, skb);
		if (!size)
		goto out;
		}

		if (skb->len < size_goal \|\| (flags & MSG_OOB))
		continue;
		@@ -987,8 +985,11 @@ wait_for_memory:
		}

		out:
		if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
		if (copied) {
		tcp_tx_timestamp(sk, sk->sk_tsflags, tcp_write_queue_tail(sk));
		if (!(flags & MSG_SENDPAGE_NOTLAST))
		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
		}
		return copied;

		do_error:
		@@ -1281,7 +1282,6 @@ new_segment:

		copied += copy;
		if (!msg_data_left(msg)) {
		tcp_tx_timestamp(sk, sockc.tsflags, skb);
		if (unlikely(flags & MSG_EOR))
		TCP_SKB_CB(skb)->eor = 1;
		goto out;
		@@ -1312,8 +1312,10 @@ wait_for_memory:
		}

		out:
		if (copied)
		if (copied) {
		tcp_tx_timestamp(sk, sockc.tsflags, tcp_write_queue_tail(sk));
		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
		}
		out_nopush:
		release_sock(sk);
		return copied + copied_syn;

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