From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: [PATCH net] tcp: fix potential underestimation on rcv_rtt Date: Tue, 12 Dec 2017 16:28:58 -0800 Message-ID: <20171213002858.74188-1-tracywwnj@gmail.com> Cc: Eric Dumazet , Wei Wang To: David Miller , netdev@vger.kernel.org Return-path: Received: from mail-it0-f65.google.com ([209.85.214.65]:34785 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752766AbdLMA3K (ORCPT ); Tue, 12 Dec 2017 19:29:10 -0500 Received: by mail-it0-f65.google.com with SMTP id m11so19263377iti.1 for ; Tue, 12 Dec 2017 16:29:09 -0800 (PST) Sender: netdev-owner@vger.kernel.org List-ID: From: Wei Wang When ms timestamp is used, current logic uses 1us in tcp_rcv_rtt_update() when the real rcv_rtt is within 1 - 999us. This could cause rcv_rtt underestimation. Fix it by always using a min value of 1ms if ms timestamp is used. Fixes: 645f4c6f2ebd ("tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps") Signed-off-by: Wei Wang Signed-off-by: Eric Dumazet --- net/ipv4/tcp_input.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 9550cc42de2d..45f750e85714 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -508,9 +508,6 @@ static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) u32 new_sample = tp->rcv_rtt_est.rtt_us; long m = sample; - if (m == 0) - m = 1; - if (new_sample != 0) { /* If we sample in larger samples in the non-timestamp * case, we could grossly overestimate the RTT especially @@ -547,6 +544,8 @@ static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) return; delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time); + if (!delta_us) + delta_us = 1; tcp_rcv_rtt_update(tp, delta_us, 1); new_measure: @@ -563,8 +562,11 @@ static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, (TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) { u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr; - u32 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ); + u32 delta_us; + if (!delta) + delta = 1; + delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ); tcp_rcv_rtt_update(tp, delta_us, 0); } } -- 2.15.1.424.g9478a66081-goog