From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neal Cardwell Subject: [PATCH net] tcp_bbr: fix to zero idle_restart only upon S/ACKed data Date: Tue, 1 May 2018 21:45:41 -0400 Message-ID: <20180502014541.194259-1-ncardwell@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: netdev@vger.kernel.org, Neal Cardwell , Yuchung Cheng , Soheil Hassas Yeganeh , Priyaranjan Jha , Yousuk Seung To: davem@davemloft.net, netdev@vger.kernel.org, ncardwell@google.com, ycheng@google.com, soheil@google.com, priyarjha@google.com, ysseung@google.com Return-path: Received: from mail-yw0-f201.google.com ([209.85.161.201]:55178 "EHLO mail-yw0-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750859AbeEBBpq (ORCPT ); Tue, 1 May 2018 21:45:46 -0400 Received: by mail-yw0-f201.google.com with SMTP id x190-v6so258963ywg.21 for ; Tue, 01 May 2018 18:45:46 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Previously the bbr->idle_restart tracking was zeroing out the bbr->idle_restart bit upon ACKs that did not SACK or ACK anything, e.g. receiving incoming data or receiver window updates. In such situations BBR would forget that this was a restart-from-idle situation, and if the min_rtt had expired it would unnecessarily enter PROBE_RTT (even though we were actually restarting from idle but had merely forgotten that fact). The fix is simple: we need to remember we are restarting from idle until we receive a S/ACK for some data (a S/ACK for the first flight of data we send as we are restarting). This commit is a stable candidate for kernels back as far as 4.9. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Priyaranjan Jha Signed-off-by: Yousuk Seung --- net/ipv4/tcp_bbr.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 158d105e76da1..58e2f479ffb4d 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -806,7 +806,9 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) } } } - bbr->idle_restart = 0; + /* Restart after idle ends only once we process a new S/ACK for data */ + if (rs->delivered > 0) + bbr->idle_restart = 0; } static void bbr_update_model(struct sock *sk, const struct rate_sample *rs) -- 2.17.0.441.gb46fe60e1d-goog