From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAA8CC433E0 for ; Thu, 30 Jul 2020 08:16:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B32022074B for ; Thu, 30 Jul 2020 08:16:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1596096999; bh=ilGqjrdiwmTB3oPnFToLZvo+G1GOh4k9YkxlamvhKQ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=SvrnKUFA8FDhl7hfawaxc7Btz9S+XiC4QsUzAiKpYD9hfzeWXujUYYt+wJwlzR7TL vi7XyzNt7iuM2roeFoRvgyjDH3wQD9G5Z1fc0MaUQDyEykRWVlX8B/NPDHQo7AR2Vv Ieiu1wcS1kkwhpchYkj36lfCBHnCFBX9CygI0ie4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730144AbgG3IQi (ORCPT ); Thu, 30 Jul 2020 04:16:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:49706 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729223AbgG3IKm (ORCPT ); Thu, 30 Jul 2020 04:10:42 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1168320838; Thu, 30 Jul 2020 08:10:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1596096641; bh=ilGqjrdiwmTB3oPnFToLZvo+G1GOh4k9YkxlamvhKQ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0P0LuGVnP0LreVfL80et9HoeUWgvzYs3PIl5kGV0mBRdyjYOKWKOSYQFKVCWW3MvE Kuw6Gqo44ZhBVDUoMCFEW0jBcRqwZjpd+xRChr8nZHeLMygD/e1d9zjmaNUd16Iu1e eNQSJIluzPUtOftSImNKzvknr9YkNrRHZX0/GiC0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Yuchung Cheng , Neal Cardwell , Eric Dumazet , "David S. Miller" Subject: [PATCH 4.9 53/61] tcp: allow at most one TLP probe per flight Date: Thu, 30 Jul 2020 10:05:11 +0200 Message-Id: <20200730074423.402710886@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200730074420.811058810@linuxfoundation.org> References: <20200730074420.811058810@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yuchung Cheng [ Upstream commit 76be93fc0702322179bb0ea87295d820ee46ad14 ] Previously TLP may send multiple probes of new data in one flight. This happens when the sender is cwnd limited. After the initial TLP containing new data is sent, the sender receives another ACK that acks partial inflight. It may re-arm another TLP timer to send more, if no further ACK returns before the next TLP timeout (PTO) expires. The sender may send in theory a large amount of TLP until send queue is depleted. This only happens if the sender sees such irregular uncommon ACK pattern. But it is generally undesirable behavior during congestion especially. The original TLP design restrict only one TLP probe per inflight as published in "Reducing Web Latency: the Virtue of Gentle Aggression", SIGCOMM 2013. This patch changes TLP to send at most one probe per inflight. Note that if the sender is app-limited, TLP retransmits old data and did not have this issue. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/tcp.h | 4 +++- net/ipv4/tcp_input.c | 11 ++++++----- net/ipv4/tcp_output.c | 13 ++++++++----- 3 files changed, 17 insertions(+), 11 deletions(-) --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -218,6 +218,8 @@ struct tcp_sock { u8 reord; /* reordering detected */ } rack; u16 advmss; /* Advertised MSS */ + u8 tlp_retrans:1, /* TLP is a retransmission */ + unused_1:7; u8 rate_app_limited:1, /* rate_{delivered,interval_us} limited? */ is_sack_reneg:1, /* in recovery from loss with SACK reneg? */ unused:6; @@ -234,7 +236,7 @@ struct tcp_sock { syn_data_acked:1,/* data in SYN is acked by SYN-ACK */ save_syn:1, /* Save headers of SYN packet */ is_cwnd_limited:1;/* forward progress limited by snd_cwnd? */ - u32 tlp_high_seq; /* snd_nxt at the time of TLP retransmit. */ + u32 tlp_high_seq; /* snd_nxt at the time of TLP */ /* RTT measurement */ u32 srtt_us; /* smoothed round trip time << 3 in usecs */ --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3566,10 +3566,8 @@ static void tcp_replace_ts_recent(struct } } -/* This routine deals with acks during a TLP episode. - * We mark the end of a TLP episode on receiving TLP dupack or when - * ack is after tlp_high_seq. - * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe. +/* This routine deals with acks during a TLP episode and ends an episode by + * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack */ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag) { @@ -3578,7 +3576,10 @@ static void tcp_process_tlp_ack(struct s if (before(ack, tp->tlp_high_seq)) return; - if (flag & FLAG_DSACKING_ACK) { + if (!tp->tlp_retrans) { + /* TLP of new data has been acknowledged */ + tp->tlp_high_seq = 0; + } else if (flag & FLAG_DSACKING_ACK) { /* This DSACK means original and TLP probe arrived; no loss */ tp->tlp_high_seq = 0; } else if (after(ack, tp->tlp_high_seq)) { --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2357,6 +2357,11 @@ void tcp_send_loss_probe(struct sock *sk int pcount; int mss = tcp_current_mss(sk); + /* At most one outstanding TLP */ + if (tp->tlp_high_seq) + goto rearm_timer; + + tp->tlp_retrans = 0; skb = tcp_send_head(sk); if (skb) { if (tcp_snd_wnd_test(tp, skb, mss)) { @@ -2379,10 +2384,6 @@ void tcp_send_loss_probe(struct sock *sk return; } - /* At most one outstanding TLP retransmission. */ - if (tp->tlp_high_seq) - goto rearm_timer; - if (skb_still_in_host_queue(sk, skb)) goto rearm_timer; @@ -2403,10 +2404,12 @@ void tcp_send_loss_probe(struct sock *sk if (__tcp_retransmit_skb(sk, skb, 1)) goto rearm_timer; + tp->tlp_retrans = 1; + +probe_sent: /* Record snd_nxt for loss detection. */ tp->tlp_high_seq = tp->snd_nxt; -probe_sent: NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES); /* Reset s.t. tcp_rearm_rto will restart timer from now */ inet_csk(sk)->icsk_pending = 0;