From owner-freebsd-net@freebsd.org Wed Aug 19 12:48:55 2020 Return-Path: Delivered-To: freebsd-net@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 7EAE83BD7FF for ; Wed, 19 Aug 2020 12:48:55 +0000 (UTC) (envelope-from l.tian.email@gmail.com) Received: from mail-ed1-x52a.google.com (mail-ed1-x52a.google.com [IPv6:2a00:1450:4864:20::52a]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4BWndy4v5xz3VvQ for ; Wed, 19 Aug 2020 12:48:54 +0000 (UTC) (envelope-from l.tian.email@gmail.com) Received: by mail-ed1-x52a.google.com with SMTP id cq28so17995290edb.10 for ; Wed, 19 Aug 2020 05:48:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=SiEu3ZtKixmr/gvDHU0+bsY7cxeaXaMulNDZl0ukUc8=; b=Q8B/44A/5Wku38Os4ALvtC6UVC3yXAp81WlJuljkGxMWLUIiriaHdmnkAyfCPoxcdN xblP5EAOTM8vi17YSW32gGPOofo+wJVwoTzpv3FkEEX1rkRKp8pue52uTCh/sHzRQuSy FYgeXb35qp4tmBVY1epsMh7B4d+w4sNOabZwMKGXqm4ZD048c8K77HTtyv/5YvBuaXa1 rZkfEGUjOpliNFFdVzsq4p2KZYqOkEINrU3oP5z62GqX8U9Cn1SaGCi/HtSFNy/U5Hjc RGsSBpMIDsEnfEA12WFx7vLU37PRdkf8/eWpLzV9Qx9TbZkT7/WpSQDe1opXzZHX7WzY 7x8A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=SiEu3ZtKixmr/gvDHU0+bsY7cxeaXaMulNDZl0ukUc8=; b=hcikRV+TkkIE3HUsuoGQYG5E4f1+KI1zriIKGEgEXTrK36AhXN7/29RMwJzUKlYKY0 jI4j+E4y2akMFvlii5bikafYet56iJlF2tcwlOnucuXfgDSow82nTZU4sVUjJ3yM54bC rnHssytfls8Eba+ewly/cO3A9ov9zwvNExYWTOfqyDJA5mAC8WYwEG9EzUB/8zZV4Ffm Wi6ZiIeLkVD8cS5mE3My4PlOHAqibGBEOwYb2WJKCKR4aVh+nXlfBBQfzgi5OhjsvVJc JZT5ribmD8z3OddV1FYf5ZwCcmqVchQ5tItuB5PnHyzXHPiz7h7Y3zn924OpilvaIt83 XOTw== X-Gm-Message-State: AOAM532yYErbZm0VmMbZDD+eypiBdgSg9cLMTQu0wBxVEIFXXOMlQLZz P7wEOj9v9GuNbleiLed4ICAsjoq47bFkb/RbcSVVhnLt X-Google-Smtp-Source: ABdhPJxI9FBhlJc9Vfa04slT7AxNdafqa1W5V5+zBI8x5IS8RaSr174UhK1WzwOj7m2bEFCFsJ0RrTa1DVFoO5icKCA= X-Received: by 2002:aa7:cd46:: with SMTP id v6mr23231795edw.21.1597841332835; Wed, 19 Aug 2020 05:48:52 -0700 (PDT) MIME-Version: 1.0 References: <51C01869-3FC2-43A8-AC9D-4A6F961F93B7@lurchi.franken.de> In-Reply-To: <51C01869-3FC2-43A8-AC9D-4A6F961F93B7@lurchi.franken.de> From: Liang Tian Date: Wed, 19 Aug 2020 08:48:41 -0400 Message-ID: Subject: Re: Appropriate Byte Counting during Congestion Avoidance To: Michael Tuexen Cc: freebsd-net Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 4BWndy4v5xz3VvQ X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=Q8B/44A/; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of ltianemail@gmail.com designates 2a00:1450:4864:20::52a as permitted sender) smtp.mailfrom=ltianemail@gmail.com X-Spamd-Result: default: False [-1.53 / 15.00]; ARC_NA(0.00)[]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com:dkim]; R_SPF_ALLOW(-0.20)[+ip6:2a00:1450:4000::/36:c]; FREEMAIL_FROM(0.00)[gmail.com]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-net@freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TO_DN_ALL(0.00)[]; DKIM_TRACE(0.00)[gmail.com:+]; RCPT_COUNT_TWO(0.00)[2]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; RCVD_IN_DNSWL_NONE(0.00)[2a00:1450:4864:20::52a:from]; NEURAL_HAM_SHORT(-0.53)[-0.534]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US]; TAGGED_FROM(0.00)[]; MAILMAN_DEST(0.00)[freebsd-net]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Aug 2020 12:48:55 -0000 Great, thanks! On Wed, Aug 19, 2020 at 4:14 AM Michael Tuexen wrote: > > > On 19. Aug 2020, at 06:51, Liang Tian wrote: > > > > Hi everyone, > > > > We noticed CWND is growing much slower than expected during congestion > > avoidance with new reno, and we came to this piece of code in > > cc_ack_received() at tcp_input.c:353 > > > > if (type == CC_ACK) { > > .... > > if (tp->snd_cwnd > tp->snd_ssthresh) { > > tp->t_bytes_acked += min(tp->ccv->bytes_this_ack, > > nsegs * V_tcp_abc_l_var * tcp_maxseg(tp)); > > if (tp->t_bytes_acked >= tp->snd_cwnd) { > > tp->t_bytes_acked -= tp->snd_cwnd; > > tp->ccv->flags |= CCF_ABC_SENTAWND; > > } > > The increment of t_bytes_acked is capped at 2*maxseg. > > The description of the sysctl variable tcp_abc_l_var(default value 2) is > > "Cap the max cwnd increment during slow-start to this number of segments" > > After reading RFC3465, it doesn't look like this cap should be applied > > here since this is clearly not during slow-start. > > We've seen in some cases the receiver is ACKing every 16 packets, and > > CWND is growing at 1/8 of the expected rate because of this. > > > > I would appreciate your opinion on this. Thanks a lot. > Hi Liang, > > thanks for bringing this up. I agree. A patch is under review: > https://reviews.freebsd.org/D26120 > > Best regards > Michael > > > > Regards, > > Liang > > _______________________________________________ > > freebsd-net@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-net > > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >