From patchwork Tue May 11 12:04:17 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leonard Crestez X-Patchwork-Id: 434736 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, 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 C82EFC43470 for ; Tue, 11 May 2021 12:04:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99F826186A for ; Tue, 11 May 2021 12:04:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231575AbhEKMFx (ORCPT ); Tue, 11 May 2021 08:05:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44046 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231359AbhEKMFr (ORCPT ); Tue, 11 May 2021 08:05:47 -0400 Received: from mail-ed1-x52a.google.com (mail-ed1-x52a.google.com [IPv6:2a00:1450:4864:20::52a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1CD7BC061574; Tue, 11 May 2021 05:04:40 -0700 (PDT) Received: by mail-ed1-x52a.google.com with SMTP id s6so22514200edu.10; Tue, 11 May 2021 05:04:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=hJsw+lxKd2cb0b24j+83WH1uLaEto1TRoqJQ5s2GyQw=; b=pFbmxPia6cPDL8Awb5a8lY1GeCvq/Eu7I5OzOoAHLtTDi8T1o+s1QGH+lj1+2gNyyG 5DlTjRd7pV8so+YSUx3Vy8B+WAP+CpMbHowMpq9jmXE7qkd7uLOVPlcyuwVgpyknjBMY pv50pn21wdpei/HpSx4eRW4mJyy59+6dLfeBZhCOlO9gbc45Us2ixzhQgmHlkgb97JZ1 tSN+ivUdegqNdUja2P6DMPXy0nE8QS58zHY2nE7pnYTIiH0vS4CeI/A0YyAgiBtB4K7E j6VgQY5LzhY1OWTyBqUMbrlpwR/AGrkYY1VePyKvl05dl2vMkEYkcX8Aa84/iThfqVVk zJ4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=hJsw+lxKd2cb0b24j+83WH1uLaEto1TRoqJQ5s2GyQw=; b=uK6KdCTK7cO4PLs2n4Bb+KrZSaVyrKTIa0MkuXBWjZRShzfZjL/tSs7mWsvJjbRkuH 02NTdgI2+Yuww9xeSj5OrwvMsyMqE2gHOyrGcdUhjZ4JTg+lIjDbBE/Kk4gF901ar2h6 rJIWtMiJBWVeIN6mkTVxA3b4xxOpsfzBw7H0TqAgAod9fA/JdlvLhNk9iUR+Ve98fT8O qoC8F8fZiwrnL+BALK/VLVDYPVcmjj4VNNCkFKU+Yz0ZY9nqF4DLgSXVEKCGdX8n3IaG Fdf6FA+SczgGyrN7iKpB7VYQPRBZTq1K5xsiUeMFuK5DPOrz2ljMwEr5sBQtKyIh2LP1 OGiA== X-Gm-Message-State: AOAM5324bboxIMwmX1Hl05PIvQVlqpYAFzXVf9Z9kylewcbH1q1dv2aR fP4wnq7L4gcjGafXg/iPBv4= X-Google-Smtp-Source: ABdhPJwUDjbq3fzDucfBHjhDPlfU72GnCoS3a0ZLgfCQOJOaj91kTubBkerTs7LeckDpkSm+b6iSJg== X-Received: by 2002:a05:6402:1115:: with SMTP id u21mr35586687edv.383.1620734678860; Tue, 11 May 2021 05:04:38 -0700 (PDT) Received: from localhost.localdomain ([2a04:241e:502:1d80:58c4:451b:d037:737c]) by smtp.gmail.com with ESMTPSA id o20sm8212615eds.20.2021.05.11.05.04.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 May 2021 05:04:38 -0700 (PDT) From: Leonard Crestez To: Neal Cardwell , Matt Mathis Cc: "David S. Miller" , Eric Dumazet , Willem de Bruijn , Jakub Kicinski , Hideaki YOSHIFUJI , David Ahern , John Heffner , Leonard Crestez , Soheil Hassas Yeganeh , Roopa Prabhu , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC 2/3] tcp: Use mtu probes if RACK is enabled Date: Tue, 11 May 2021 15:04:17 +0300 Message-Id: X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org RACK allows detecting a loss in min_rtt / 4 based on just one extra packet. If enabled use this instead of relying of fast retransmit. Suggested-by: Neal Cardwell Signed-off-by: Leonard Crestez --- Documentation/networking/ip-sysctl.rst | 5 +++++ include/net/netns/ipv4.h | 1 + net/ipv4/sysctl_net_ipv4.c | 7 +++++++ net/ipv4/tcp_ipv4.c | 1 + net/ipv4/tcp_output.c | 22 +++++++++++++++++++++- 5 files changed, 35 insertions(+), 1 deletion(-) diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 108a5ee227d3..4f6ac69f61e7 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -325,10 +325,15 @@ tcp_mtu_probe_floor - INTEGER tcp_mtu_probe_autocork - BOOLEAN Take into account mtu probe size when accumulating data via autocorking. Default: 1 +tcp_mtu_probe_rack - BOOLEAN + Try to use shorter probes if RACK is also enabled + + Default: 1 + tcp_min_snd_mss - INTEGER TCP SYN and SYNACK messages usually advertise an ADVMSS option, as described in RFC 1122 and RFC 6691. If this ADVMSS option is smaller than tcp_min_snd_mss, diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h index 3a2d8bf2b20a..298e65d8605c 100644 --- a/include/net/netns/ipv4.h +++ b/include/net/netns/ipv4.h @@ -113,10 +113,11 @@ struct netns_ipv4 { u8 sysctl_tcp_l3mdev_accept; #endif u8 sysctl_tcp_mtu_probing; int sysctl_tcp_mtu_probe_floor; int sysctl_tcp_mtu_probe_autocork; + int sysctl_tcp_mtu_probe_rack; int sysctl_tcp_base_mss; int sysctl_tcp_min_snd_mss; int sysctl_tcp_probe_threshold; u32 sysctl_tcp_probe_interval; diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index e19176c17973..f9366f35ff9c 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -834,10 +834,17 @@ static struct ctl_table ipv4_net_table[] = { .data = &init_net.ipv4.sysctl_tcp_mtu_probe_autocork, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec, }, + { + .procname = "tcp_mtu_probe_rack", + .data = &init_net.ipv4.sysctl_tcp_mtu_probe_rack, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, { .procname = "tcp_probe_threshold", .data = &init_net.ipv4.sysctl_tcp_probe_threshold, .maxlen = sizeof(int), .mode = 0644, diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 7e75423c08c9..4928fcd6e233 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -2890,10 +2890,11 @@ static int __net_init tcp_sk_init(struct net *net) net->ipv4.sysctl_tcp_min_snd_mss = TCP_MIN_SND_MSS; net->ipv4.sysctl_tcp_probe_threshold = TCP_PROBE_THRESHOLD; net->ipv4.sysctl_tcp_probe_interval = TCP_PROBE_INTERVAL; net->ipv4.sysctl_tcp_mtu_probe_floor = TCP_MIN_SND_MSS; net->ipv4.sysctl_tcp_mtu_probe_autocork = 1; + net->ipv4.sysctl_tcp_mtu_probe_rack = 1; net->ipv4.sysctl_tcp_keepalive_time = TCP_KEEPALIVE_TIME; net->ipv4.sysctl_tcp_keepalive_probes = TCP_KEEPALIVE_PROBES; net->ipv4.sysctl_tcp_keepalive_intvl = TCP_KEEPALIVE_INTVL; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 5a320d792ec4..7cd1e8fd9749 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2311,27 +2311,47 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len) } return true; } +static int tcp_mtu_probe_is_rack(const struct sock *sk) +{ + struct net *net = sock_net(sk); + + return (net->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION && + net->ipv4.sysctl_tcp_mtu_probe_rack); +} + /* Calculate the size of an MTU probe * Probing the MTU requires one packets which is larger that current MSS as well * as enough following mtu-sized packets to ensure that a probe loss can be * detected without a full Retransmit Time out. */ int tcp_mtu_probe_size_needed(struct sock *sk, int *probe_size) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); int probe_size_val; int size_needed; /* This might be a little slow: */ probe_size_val = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high + icsk->icsk_mtup.search_low) >> 1); if (probe_size) *probe_size = probe_size_val; - size_needed = probe_size_val + (tp->reordering + 1) * tp->mss_cache; + + if (tcp_mtu_probe_is_rack(sk)) { + /* RACK allows recovering in min_rtt / 4 based on just one extra packet + * Use two to account for unrelated losses + */ + size_needed = probe_size_val + 2 * tp->mss_cache; + } else { + /* Without RACK send enough extra packets to trigger fast retransmit + * This is dynamic DupThresh + 1 + */ + size_needed = probe_size_val + (tp->reordering + 1) * tp->mss_cache; + } return size_needed; } /* Create a new MTU probe if we are ready. From patchwork Tue May 11 12:04:18 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leonard Crestez X-Patchwork-Id: 434735 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 F0439C43611 for ; Tue, 11 May 2021 12:04:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C28056186A for ; Tue, 11 May 2021 12:04:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231628AbhEKMF5 (ORCPT ); Tue, 11 May 2021 08:05:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231544AbhEKMFs (ORCPT ); Tue, 11 May 2021 08:05:48 -0400 Received: from mail-ej1-x633.google.com (mail-ej1-x633.google.com [IPv6:2a00:1450:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9422EC06175F; Tue, 11 May 2021 05:04:41 -0700 (PDT) Received: by mail-ej1-x633.google.com with SMTP id j10so2311237ejb.3; Tue, 11 May 2021 05:04:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=Knt9wT/TnxSJqdQUEwJzgxbl2tHLC9vQ7ygQk/z3nDU=; b=PGpkUvAz7khi0D+tBeYCLn8QramMYFE7ZaC3IEiqLoNSS5AYCDPZ+6Z4L8qCqF9rQM keG1pQW9P0ATI+GDgD2vxPQrrsK9PxpAzOMBYcuinQgqtGR5aw5y/bqI2WVDDhtzCTiO Cfv5JWO8k8xIIplo/d2mRBjSfpiyLX6o8bmbBzj3EGHBFGgLm7mtpJMSSwKbnOXh3BhL TzGlmRzCBg5gq4gzD6E/k0Z4B+MYpuGnJJgcPzqvNr9KWYJKyZEI1lq5Dy0BERIYfPbH /fbWxbkC/IYIFQ5K4tZYycnDXRk/NZgQCfKmvPo/fL1BTFlMb/DAFqPeCxpQrNJtvpiE RvoQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=Knt9wT/TnxSJqdQUEwJzgxbl2tHLC9vQ7ygQk/z3nDU=; b=GtwitcS6PdZm8VeNwdh051R9WiB942d4hriq/uLyjGKZEL8W3I6xaX2qYpCboU9Hsx HKzsvPXP2xtfIGTpgAks9jCwgwitlYgmZp/sGNVxQnvepXVAD2fKkwZcMv3WU8oF257B FXE+SVJxR44IpToziHaq+yaD6JQrVjYRTH+w3+743HAN0vBQTH66I2v1ZGKuaVg0bxLf oqglIiscmF/02y8ZiUe7rI3nL3pmNYMJJcxa8SaTfXdmO+gfFswuqbnho1u9o7eM5baV jrc4sWRRRbXTtBOSay3QO0QvLtDAOh0LuMjP1rKSgW2HzXcy4MjIXCf725p8kBnLMJKK eSFw== X-Gm-Message-State: AOAM533BcYWX26cXlBOfiRLmhe+rdIqUYphuqN7t+Cpyet0GXqecTPWR 08s1PM8wkDfodxF6X6tpA1A= X-Google-Smtp-Source: ABdhPJylTaR0NiP5BrjYnLaUYJlc0wK+5kK1MkfSHIaFHaMnlcGnee8r11i4PaXZT4LNffxHCooJHQ== X-Received: by 2002:a17:906:2ec6:: with SMTP id s6mr7755049eji.65.1620734680276; Tue, 11 May 2021 05:04:40 -0700 (PDT) Received: from localhost.localdomain ([2a04:241e:502:1d80:58c4:451b:d037:737c]) by smtp.gmail.com with ESMTPSA id o20sm8212615eds.20.2021.05.11.05.04.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 May 2021 05:04:39 -0700 (PDT) From: Leonard Crestez To: Neal Cardwell , Matt Mathis Cc: "David S. Miller" , Eric Dumazet , Willem de Bruijn , Jakub Kicinski , Hideaki YOSHIFUJI , David Ahern , John Heffner , Leonard Crestez , Soheil Hassas Yeganeh , Roopa Prabhu , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC 3/3] tcp: Adjust congestion window handling for mtu probe Date: Tue, 11 May 2021 15:04:18 +0300 Message-Id: <1d5beaabad348d16a95fc5e699f87f3248758996.1620733594.git.cdleonard@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org When preparing an mtu probe linux checks for snd_cwnd >= 11 and for 2 more packets to fit alongside what is currently in flight. The reasoning behind these constants is unclear. Replace this with checks based on the required probe size: * Skip probing if congestion window is too small to ever fit a probe. * Wait for the congestion window to drain if too many packets are already in flight. This is very similar to snd_wnd logic except packets are counted instead of bytes. This patch will allow mtu probing at smaller cwnd values. On very fast links after successive succesful MTU probes the cwnd (measured in packets) shrinks and does not grow again because tcp_is_cwnd_limited returns false. If snd_cwnd falls below then no more probes are sent despite the link being otherwise idle. Signed-off-by: Leonard Crestez --- net/ipv4/tcp_output.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 7cd1e8fd9749..ccf3eb29e7a5 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2369,10 +2369,11 @@ static int tcp_mtu_probe(struct sock *sk) struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb, *nskb, *next; struct net *net = sock_net(sk); int probe_size; int size_needed; + int packets_needed; int copy, len; int mss_now; int interval; /* Not currently probing/verifying, @@ -2381,20 +2382,20 @@ static int tcp_mtu_probe(struct sock *sk) * not SACKing (the variable headers throw things off) */ if (likely(!icsk->icsk_mtup.enabled || icsk->icsk_mtup.probe_size || inet_csk(sk)->icsk_ca_state != TCP_CA_Open || - tp->snd_cwnd < 11 || tp->rx_opt.num_sacks || tp->rx_opt.dsack)) return -1; /* Use binary search for probe_size between tcp_mss_base, * and current mss_clamp. if (search_high - search_low) * smaller than a threshold, backoff from probing. */ mss_now = tcp_current_mss(sk); size_needed = tcp_mtu_probe_size_needed(sk, &probe_size); + packets_needed = DIV_ROUND_UP(size_needed, tp->mss_cache); interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low; /* When misfortune happens, we are reprobing actively, * and then reprobe timer has expired. We stick with current * probing process by not resetting search range to its orignal. @@ -2406,26 +2407,26 @@ static int tcp_mtu_probe(struct sock *sk) */ tcp_mtu_check_reprobe(sk); return -1; } + /* Can probe fit inside snd_cwnd */ + if (packets_needed > tp->snd_cwnd) + return -1; + /* Have enough data in the send queue to probe? */ if (tp->write_seq - tp->snd_nxt < size_needed) return net->ipv4.sysctl_tcp_mtu_probe_autocork ? 0 : -1; if (tp->snd_wnd < size_needed) return -1; if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp))) return 0; - /* Do we need to wait to drain cwnd? With none in flight, don't stall */ - if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) { - if (!tcp_packets_in_flight(tp)) - return -1; - else - return 0; - } + /* Wait for snd_cwnd to drain */ + if (tcp_packets_in_flight(tp) + packets_needed > tp->snd_cwnd) + return 0; if (!tcp_can_coalesce_send_queue_head(sk, probe_size)) return -1; /* We're allowed to probe. Build it now. */