tcp: use tcp_jiffies32 to feed tp->snd_cwnd_stamp

Use tcp_jiffies32 instead of tcp_time_stamp to feed
tp->snd_cwnd_stamp.

tcp_time_stamp will soon be a litle bit more expensive
than simply reading 'jiffies'.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index be9f8f4..4bd50f0 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -151,7 +151,7 @@ void tcp_cwnd_restart(struct sock *sk, s32 delta)
 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
 		cwnd >>= 1;
 	tp->snd_cwnd = max(cwnd, restart_cwnd);
-	tp->snd_cwnd_stamp = tcp_time_stamp;
+	tp->snd_cwnd_stamp = tcp_jiffies32;
 	tp->snd_cwnd_used = 0;
 }
 
@@ -1576,7 +1576,7 @@ static void tcp_cwnd_application_limited(struct sock *sk)
 		}
 		tp->snd_cwnd_used = 0;
 	}
-	tp->snd_cwnd_stamp = tcp_time_stamp;
+	tp->snd_cwnd_stamp = tcp_jiffies32;
 }
 
 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
@@ -1597,14 +1597,14 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
 	if (tcp_is_cwnd_limited(sk)) {
 		/* Network is feed fully. */
 		tp->snd_cwnd_used = 0;
-		tp->snd_cwnd_stamp = tcp_time_stamp;
+		tp->snd_cwnd_stamp = tcp_jiffies32;
 	} else {
 		/* Network starves. */
 		if (tp->packets_out > tp->snd_cwnd_used)
 			tp->snd_cwnd_used = tp->packets_out;
 
 		if (sysctl_tcp_slow_start_after_idle &&
-		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
+		    (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
 		    !ca_ops->cong_control)
 			tcp_cwnd_application_limited(sk);