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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 0F999C33CB3 for ; Wed, 15 Jan 2020 06:59:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DAD1D24679 for ; Wed, 15 Jan 2020 06:59:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726566AbgAOG7Y convert rfc822-to-8bit (ORCPT ); Wed, 15 Jan 2020 01:59:24 -0500 Received: from mail.wangsu.com ([123.103.51.227]:35101 "EHLO wangsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725999AbgAOG7X (ORCPT ); Wed, 15 Jan 2020 01:59:23 -0500 Received: from XMCDN1207038 (unknown [59.61.78.137]) by app2 (Coremail) with SMTP id 4zNnewD3_2c2uB5ehaIJAA--.229S2; Wed, 15 Jan 2020 14:59:03 +0800 (CST) From: "Pengcheng Yang" To: "'Yuchung Cheng'" , "'Eric Dumazet'" Cc: "'David Miller'" , "'Alexey Kuznetsov'" , "'Hideaki YOSHIFUJI'" , "'Alexei Starovoitov'" , "'Daniel Borkmann'" , "'Martin KaFai Lau'" , "'Song Liu'" , "'Yonghong Song'" , , "'netdev'" , "'LKML'" References: <1578993820-2114-1-git-send-email-yangpc@wangsu.com> In-Reply-To: Subject: RE: [PATCH] tcp: fix marked lost packets not being retransmitted Date: Wed, 15 Jan 2020 14:58:40 +0800 Message-ID: <019a01d5cb71$38e8edf0$aabac9d0$@wangsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQHDr2WaWgeAzMrHi25Ee74mw556twFOsMkmAiFKdhOn9AMwwA== Content-Language: zh-cn X-CM-TRANSID: 4zNnewD3_2c2uB5ehaIJAA--.229S2 X-Coremail-Antispam: 1UD129KBjvJXoWxJw17tw1DWw4ruFyDWw48Zwb_yoWrGFWkpa 1rKFnrtFs8Jr1Fkw1DtrWUXry8tFWSy345W3sYyr9Iyws8tr13uF15t3y3KFy3WF48Aw40 qF4jyw13Was8AFDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkGb7Iv0xC_tr1lb4IE77IF4wAFc2x0x2IEx4CE42xK8VAvwI8I cIk0rVWrJVCq3wA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK021l84ACjcxK6xIIjx v20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26rxl6s0DM28EF7xvwVC2 z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v26rxl6s0DM2AIxVAIcxkEcV Aq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMcIj6x8ErcxFaVAv8VW8GwAv 7VCY1x0262k0Y48FwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI4 8JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkIecxEwVAFwVW8AwCF04k20xvY0x0EwIxGrwCF 04k20xvE74AGY7Cv6cx26r48MxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI 0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y 0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxV W8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Zr0_Wr1UMIIF0xvEx4A2jsIE14v26r1j6r4U MIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07UhjjgUUU UU= X-CM-SenderInfo: p1dqw1nf6zt0xjvxhudrp/ Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Jan 15, 2020 at 2:40 AM Yuchung Cheng wrote: > > On Tue, Jan 14, 2020 at 8:06 AM Eric Dumazet > wrote: > > > > On Tue, Jan 14, 2020 at 1:24 AM Pengcheng Yang > wrote: > > > > > > When the packet pointed to by retransmit_skb_hint is unlinked by ACK, > > > retransmit_skb_hint will be set to NULL in tcp_clean_rtx_queue(). > > > If packet loss is detected at this time, retransmit_skb_hint will be set > > > to point to the current packet loss in tcp_verify_retransmit_hint(), > > > then the packets that were previously marked lost but not retransmitted > > > due to the restriction of cwnd will be skipped and cannot be > > > retransmitted. > > > > > > "cannot be retransmittted" sounds quite alarming. > > > > You meant they will eventually be retransmitted, or that the flow is > > completely frozen at this point ? > He probably means those lost packets will be skipped until a timeout > that reset hint pointer. nice fix this would save some RTOs. Yes, I mean those packets will not be retransmitted until RTO. I'm sorry I didn't describe it clearly. > > > > > Thanks for the fix and test ! > > > > (Not sure why you CC all these people having little TCP expertise btw) Maybe I should CC fewer people :) > > > > > To fix this, when retransmit_skb_hint is NULL, retransmit_skb_hint can > > > be reset only after all marked lost packets are retransmitted > > > (retrans_out >= lost_out), otherwise we need to traverse from > > > tcp_rtx_queue_head in tcp_xmit_retransmit_queue(). > > > > > > Packetdrill to demonstrate: > > > > > > // Disable RACK and set max_reordering to keep things simple > > > 0 `sysctl -q net.ipv4.tcp_recovery=0` > > > +0 `sysctl -q net.ipv4.tcp_max_reordering=3` > > > > > > // Establish a connection > > > +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 > > > +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 > > > +0 bind(3, ..., ...) = 0 > > > +0 listen(3, 1) = 0 > > > > > > +.1 < S 0:0(0) win 32792 > > > +0 > S. 0:0(0) ack 1 <...> > > > +.01 < . 1:1(0) ack 1 win 257 > > > +0 accept(3, ..., ...) = 4 > > > > > > // Send 8 data segments > > > +0 write(4, ..., 8000) = 8000 > > > +0 > P. 1:8001(8000) ack 1 > > > > > > // Enter recovery and 1:3001 is marked lost > > > +.01 < . 1:1(0) ack 1 win 257 > > > +0 < . 1:1(0) ack 1 win 257 > > > +0 < . 1:1(0) ack 1 win 257 > > > > > > // Retransmit 1:1001, now retransmit_skb_hint points to 1001:2001 > > > +0 > . 1:1001(1000) ack 1 > > > > > > // 1001:2001 was ACKed causing retransmit_skb_hint to be set to NULL > > > +.01 < . 1:1(0) ack 2001 win 257 > > > // Now retransmit_skb_hint points to 4001:5001 which is now marked lost > > > > > > // BUG: 2001:3001 was not retransmitted > > > +0 > . 2001:3001(1000) ack 1 > > > > > > Signed-off-by: Pengcheng Yang > > > --- > > > net/ipv4/tcp_input.c | 7 ++++--- > > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > > index 0238b55..5347ab2 100644 > > > --- a/net/ipv4/tcp_input.c > > > +++ b/net/ipv4/tcp_input.c > > > @@ -915,9 +915,10 @@ static void tcp_check_sack_reordering(struct sock > *sk, const u32 low_seq, > > > /* This must be called before lost_out is incremented */ > > > static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff > *skb) > > > { > > > - if (!tp->retransmit_skb_hint || > > > - before(TCP_SKB_CB(skb)->seq, > > > - TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) > > > + if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) > || > > > + (tp->retransmit_skb_hint && > > > + before(TCP_SKB_CB(skb)->seq, > > > + TCP_SKB_CB(tp->retransmit_skb_hint)->seq))) > > > tp->retransmit_skb_hint = skb; > > > } > > > > > > -- > > > 1.8.3.1 > > >