Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755474Ab3I3KMe (ORCPT ); Mon, 30 Sep 2013 06:12:34 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:43550 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755439Ab3I3KM3 (ORCPT ); Mon, 30 Sep 2013 06:12:29 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Eric Dumazet , Neal Cardwell , Yuchung Cheng , "David S. Miller" , Luis Henriques Subject: [PATCH 044/104] tcp: cubic: fix bug in bictcp_acked() Date: Mon, 30 Sep 2013 11:10:21 +0100 Message-Id: <1380535881-9239-45-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.8.3.2 In-Reply-To: <1380535881-9239-1-git-send-email-luis.henriques@canonical.com> References: <1380535881-9239-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1986 Lines: 55 3.5.7.22 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit cd6b423afd3c08b27e1fed52db828ade0addbc6b upstream. While investigating about strange increase of retransmit rates on hosts ~24 days after boot, Van found hystart was disabled if ca->epoch_start was 0, as following condition is true when tcp_time_stamp high order bit is set. (s32)(tcp_time_stamp - ca->epoch_start) < HZ Quoting Van : At initialization & after every loss ca->epoch_start is set to zero so I believe that the above line will turn off hystart as soon as the 2^31 bit is set in tcp_time_stamp & hystart will stay off for 24 days. I think we've observed that cubic's restart is too aggressive without hystart so this might account for the higher drop rate we observe. Diagnosed-by: Van Jacobson Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Luis Henriques --- net/ipv4/tcp_cubic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index b6b591f..b6ae92a 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -416,7 +416,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) return; /* Discard delay samples right after fast recovery */ - if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) + if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ) return; delay = (rtt_us << 3) / USEC_PER_MSEC; -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/