netdev - [PATCH net-next] tcp: remove conditional branches from tcp_mstamp

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Message-Id: <20190322132629.158360-1-edumazet@google.com>
Date:   Fri, 22 Mar 2019 06:26:29 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next] tcp: remove conditional branches from tcp_mstamp_refresh()

tcp_clock_ns() (aka ktime_get_ns()) is using monotonic clock,
so the checks we had in tcp_mstamp_refresh() are no longer
relevant.

This patch removes cpu stall (when the cache line is not hot)

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp_output.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 4522579aaca2d24b7be61abac658a3c8cbd2b960..e265d1aeeb66996da3903eef383eaec9a320cce0 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -52,12 +52,8 @@ void tcp_mstamp_refresh(struct tcp_sock *tp)
 {
 	u64 val = tcp_clock_ns();
 
-	if (val > tp->tcp_clock_cache)
-		tp->tcp_clock_cache = val;
-
-	val = div_u64(val, NSEC_PER_USEC);
-	if (val > tp->tcp_mstamp)
-		tp->tcp_mstamp = val;
+	tp->tcp_clock_cache = val;
+	tp->tcp_mstamp = div_u64(val, NSEC_PER_USEC);
 }
 
 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
-- 
2.21.0.392.gf8f6787159e-goog