tcp: instrument how long TCP is busy sending

This patch measures TCP busy time, which is defined as the period
of time when sender has data (or FIN) to send. The time starts when
data is buffered and stops when the write queue is flushed by ACKs
or error events.

Note the busy time does not include SYN time, unless data is
included in SYN (i.e. Fast Open). It does include FIN time even
if the FIN carries no payload. Excluding pure FIN is possible but
would incur one additional test in the fast path, which may not
be worth it.

Signed-off-by: Francis Yan <francisyyan@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e5ff4083870d..3e097e39d4d2 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1535,6 +1535,7 @@ static inline void tcp_write_queue_purge(struct sock *sk)
 {
         struct sk_buff *skb;
 
+        tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
                 sk_wmem_free_skb(sk, skb);
         sk_mem_reclaim(sk);
@@ -1593,8 +1594,10 @@ static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *
 
 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
 {
-        if (sk->sk_send_head == skb_unlinked)
+        if (sk->sk_send_head == skb_unlinked) {
                 sk->sk_send_head = NULL;
+                tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
+        }
         if (tcp_sk(sk)->highest_sack == skb_unlinked)
                 tcp_sk(sk)->highest_sack = NULL;
 }
@@ -1616,6 +1619,7 @@ static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb
         /* Queue it, remembering where we must start sending. */
         if (sk->sk_send_head == NULL) {
                 sk->sk_send_head = skb;
+                tcp_chrono_start(sk, TCP_CHRONO_BUSY);
 
                 if (tcp_sk(sk)->highest_sack == NULL)
                         tcp_sk(sk)->highest_sack = skb;