From patchwork Tue Jul 7 04:22:06 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jon Maxwell X-Patchwork-Id: 492033 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id CD02D1402C9 for ; Tue, 7 Jul 2015 14:22:55 +1000 (AEST) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b=V09lWv+a; dkim-atps=neutral Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751154AbbGGEWm (ORCPT ); Tue, 7 Jul 2015 00:22:42 -0400 Received: from mail-qg0-f53.google.com ([209.85.192.53]:33488 "EHLO mail-qg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146AbbGGEWi (ORCPT ); Tue, 7 Jul 2015 00:22:38 -0400 Received: by qgef3 with SMTP id f3so29166658qge.0; Mon, 06 Jul 2015 21:22:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id; bh=j4Wq0PaJzpztc+EdBMIWFWn1OQOECixEEqUg7q+k3kg=; b=V09lWv+a6Kf7AFh6m1XGXZwb4PNP1W4uzoJd8Ie/vO1IEK4NqLAZ3Chx+0l0MWct3c YkjtiBwRT5k4+EmQPV6imLmBFiV1TLlRevStJcNZSzSE67/T8uAFd+/S59W1IDgy1MDQ RLBlh3QO8nfeBZzqoxgj0GbirUSOF53XBzsVyPsDSt6tfwmGtodVEjomTHcZo30CP8ev hyc1qpGYgB4M/nBGD5tgD9U6NdzKEvlf7LxSyobMO53N4EVGP2VLVCiOCoxT7vjZi6Xk C5KZtD76gYqBdx9fw/bZpNzUS0/TmNtE93t+U1msM8skyRGvs540/uFrlPxzGhvgIvTy WnuA== X-Received: by 10.55.50.195 with SMTP id y186mr3737884qky.55.1436242958157; Mon, 06 Jul 2015 21:22:38 -0700 (PDT) Received: from dhcp-1-107.bne.redhat.com (110-175-8-199.static.tpgi.com.au. [110.175.8.199]) by mx.google.com with ESMTPSA id x137sm10542515qkx.28.2015.07.06.21.22.34 (version=TLSv1.2 cipher=AES128-GCM-SHA256 bits=128/128); Mon, 06 Jul 2015 21:22:37 -0700 (PDT) From: Jon Maxwell To: davem@davemloft.net Cc: kuznet@ms2.inr.ac.ru, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jmaxwell@redhat.com, Jon Maxwell Subject: [PATCH net-next] tcp: always send a quick ack when quickacks are enabled Date: Tue, 7 Jul 2015 14:22:06 +1000 Message-Id: <1436242926-21416-1-git-send-email-jmaxwell37@gmail.com> X-Mailer: git-send-email 1.8.3.1 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org I ran some tests and after setting the "ip route change quickack 1" knob there were still many delayed ACKs sent. This occured because when icsk_ack.quick=0 the !icsk_ack.pingpong value is subsequently ignored as tcp_in_quickack_mode() checks both these values. The condition for a quick ack to trigger requires that both icsk_ack.quick != 0 and icsk_ack.pingpong=0. Currently only icsk_ack.pingpong is controlled by the knob. But the icsk_ack.quick value changes dynamically depending on heuristics. The crux of the matter is that delayed acks still cannot be entirely disabled even with the RTAX_QUICKACK per dst knob enabled. This patch ensures that a quick ack is always sent when the RTAX_QUICKACK per dst knob is turned on. The "ip route change quickack 1" knob was recently added to enable quickacks. It was modeled around the TCP_QUICKACK setsockopt() option. This issue is that even with "ip route change quickack 1" enabled we still see delayed ACKs under some conditions. It would be nice to be able to completely disable delayed ACKs. Here is an example: # netstat -s|grep dela 3 delayed acks sent For all routes enable the knob # ip route change quickack 1 Generate some traffic across a slow link and we still see the delayed acks. # netstat -s|grep dela 106 delayed acks sent 1 delayed acks further delayed because of locked socket The issue is that both the "ip route change quickack 1" knob and the TCP_QUICKACK option set the icsk_ack.pingpong variable to 0. However at the business end in the __tcp_ack_snd_check() routine, tcp_in_quickack_mode() checks that both icsk_ack.quick != 0 and icsk_ack.pingpong=0 in order to trigger a quickack. As icsk_ack.quick is determined by heuristics it can be 0. When that occurs the icsk_ack.pingpong value is ignored and a delayed ACK is sent regardless. This patch moves the RTAX_QUICKACK per dst check into the __tcp_ack_snd_check() routine which ensures that a quickack is always sent when the quickack knob is enabled for that dst. Signed-off-by: Jon Maxwell --- net/ipv4/tcp_input.c | 8 ++++---- net/ipv4/tcp_output.c | 6 ++---- 2 files changed, 6 insertions(+), 8 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 684f095..1af7d74 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3948,7 +3948,6 @@ void tcp_reset(struct sock *sk) static void tcp_fin(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); - const struct dst_entry *dst; inet_csk_schedule_ack(sk); @@ -3960,9 +3959,7 @@ static void tcp_fin(struct sock *sk) case TCP_ESTABLISHED: /* Move to CLOSE_WAIT */ tcp_set_state(sk, TCP_CLOSE_WAIT); - dst = __sk_dst_get(sk); - if (!dst || !dst_metric(dst, RTAX_QUICKACK)) - inet_csk(sk)->icsk_ack.pingpong = 1; + inet_csk(sk)->icsk_ack.pingpong = 1; break; case TCP_CLOSE_WAIT: @@ -4887,6 +4884,7 @@ static inline void tcp_data_snd_check(struct sock *sk) static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) { struct tcp_sock *tp = tcp_sk(sk); + const struct dst_entry *dst = __sk_dst_get(sk); /* More than one full frame received... */ if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && @@ -4896,6 +4894,8 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) __tcp_select_window(sk) >= tp->rcv_wnd) || /* We ACK each frame or... */ tcp_in_quickack_mode(sk) || + /* quickack on dst */ + (dst && dst_metric(dst, RTAX_QUICKACK)) || /* We have out of order data. */ (ofo_possible && skb_peek(&tp->out_of_order_queue))) { /* Then ack it now */ diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index b1c218d..7105784 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -163,7 +163,6 @@ static void tcp_event_data_sent(struct tcp_sock *tp, { struct inet_connection_sock *icsk = inet_csk(sk); const u32 now = tcp_time_stamp; - const struct dst_entry *dst = __sk_dst_get(sk); if (sysctl_tcp_slow_start_after_idle && (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto)) @@ -174,9 +173,8 @@ static void tcp_event_data_sent(struct tcp_sock *tp, /* If it is a reply for ato after last received * packet, enter pingpong mode. */ - if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato && - (!dst || !dst_metric(dst, RTAX_QUICKACK))) - icsk->icsk_ack.pingpong = 1; + if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) + icsk->icsk_ack.pingpong = 1; } /* Account for an ACK we sent. */