From nobody Thu Jul 18 16:35:46 2024 X-Original-To: freebsd-net@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4WPz2G0C98z5Rj1w for ; Thu, 18 Jul 2024 16:35:50 +0000 (UTC) (envelope-from tuexen@freebsd.org) Received: from drew.franken.de (mail-n.franken.de [193.175.24.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.franken.de", Issuer "Sectigo RSA Domain Validation Secure Server CA" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4WPz2F5xF9z4Qyw; Thu, 18 Jul 2024 16:35:49 +0000 (UTC) (envelope-from tuexen@freebsd.org) Authentication-Results: mx1.freebsd.org; none Received: from smtpclient.apple (unknown [IPv6:2a02:8109:1140:c3d:25ea:b605:4a77:64ed]) (Authenticated sender: micmac) by drew.franken.de (Postfix) with ESMTPSA id DB41E721E2817; Thu, 18 Jul 2024 18:35:46 +0200 (CEST) Content-Type: text/plain; charset=utf-8 List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@FreeBSD.org Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3774.600.62\)) Subject: Re: TCP Success Story (was Re: TCP_RACK, TCP_BBR, and firewalls) From: tuexen@freebsd.org In-Reply-To: Date: Thu, 18 Jul 2024 18:35:46 +0200 Cc: FreeBSD Net Content-Transfer-Encoding: quoted-printable Message-Id: References: To: Alan Somers X-Mailer: Apple Mail (2.3774.600.62) X-Spam-Status: No, score=-2.9 required=5.0 tests=ALL_TRUSTED,BAYES_00 autolearn=disabled version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on mail-n.franken.de X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:680, ipnet:193.174.0.0/15, country:DE] X-Rspamd-Queue-Id: 4WPz2F5xF9z4Qyw > On 18. Jul 2024, at 16:03, Alan Somers wrote: >=20 > On Wed, Jul 17, 2024 at 2:27=E2=80=AFPM wrote: >>=20 >>> On 17. Jul 2024, at 22:00, Alan Somers wrote: >>>=20 >>> On Sat, Jul 13, 2024 at 1:50=E2=80=AFAM wrote: >>>>=20 >>>>> On 13. Jul 2024, at 01:43, Alan Somers = wrote: >>>>>=20 >>>>> I've been experimenting with RACK and BBR. In my environment, = they >>>>> can dramatically improve single-stream TCP performance, which is >>>>> awesome. But pf interferes. I have to disable pf in order for = them >>>>> to work at all. >>>>>=20 >>>>> Is this a known limitation? If not, I will experiment some more = to >>>>> determine exactly what aspect of my pf configuration is = responsible. >>>>> If so, can anybody suggest what changes would have to happen to = make >>>>> the two compatible? >>>> A problem with same symptoms was already reported and fixed in >>>> https://reviews.freebsd.org/D43769 >>>>=20 >>>> Which version are you using? >>>>=20 >>>> Best regards >>>> Michael >>>>>=20 >>>>> -Alan >>>=20 >>> TLDR; tcp_rack is good, cc_chd is better, and tcp_bbr is best >>>=20 >>> I want to follow up with the list to post my conclusions. Firstly >>> tuexen@ helped me solve my problem: in FreeBSD 14.0 there is a 3-way >>> incompatibility between (tcp_bbr || tcp_rack) && lro && pf. I can >>> confirm that tcp_bbr works for me if I either disable LRO, disable = PF, >>> or switch to a 14.1 server. >>>=20 >>> Here's the real problem: on multiple production servers, downloading >>> large files (or ZFS send/recv streams) was slow. After ruling out >>> many possible causes, wireshark revealed that the connection was >>> suffering about 0.05% packet loss. I don't know the source of that >>> packet loss, but I don't believe it to be congestion-related. Along >>> with a 54ms RTT, that's a fatal combination for the throughput of >>> loss-based congestion control algorithms. According to the Mathis >>> Formula [1], I could only expect 1.1 MBps over such a connection. >>> That's actually worse than what I saw. With default settings >>> (cc_cubic), I averaged 5.6 MBps. Probably Mathis's assumptions are >>> outdated, but that's still pretty close for such a simple formula >>> that's 27 years old. >>>=20 >>> So I benchmarked all available congestion control algorithms for >>> single download streams. The results are summarized in the table >>> below. >>>=20 >>> Algo Packet Loss Rate Average Throughput >>> vegas 0.05% 2.0 MBps >>> newreno 0.05% 3.2 MBps >>> cubic 0.05% 5.6 MBps >>> hd 0.05% 8.6 MBps >>> cdg 0.05% 13.5 MBps >>> rack 0.04% 14 MBps >>> htcp 0.05% 15 MBps >>> dctcp 0.05% 15 MBps >>> chd 0.05% 17.3 MBps >>> bbr 0.05% 29.2 MBps >>> cubic 10% 159 kBps >>> chd 10% 208 kBps >>> bbr 10% 5.7 MBps >>>=20 >>> RACK seemed to achieve about the same maximum bandwidth as BBR, = though >>> it took a lot longer to get there. Also, with RACK, wireshark >>> reported about 10x as many retransmissions as dropped packets, which >>> is suspicious. >>>=20 >>> At one point, something went haywire and packet loss briefly spiked = to >>> the neighborhood of 10%. I took advantage of the chaos to repeat my >>> measurements. As the table shows, all algorithms sucked under those >>> conditions, but BBR sucked impressively less than the others. >>>=20 >>> Disclaimer: there was significant run-to-run variation; the = presented >>> results are averages. And I did not attempt to measure packet loss >>> exactly for most runs; 0.05% is merely an average of a few selected >>> runs. These measurements were taken on a production server running = a >>> real workload, which introduces noise. Soon I hope to have the >>> opportunity to repeat the experiment on an idle server in the same >>> environment. >>>=20 >>> In conclusion, while we'd like to use BBR, we really can't until we >>> upgrade to 14.1, which hopefully will be soon. So in the meantime >>> we've switched all relevant servers from cubic to chd, and we'll >>> reevaluate BBR after the upgrade. >> Hi Alan, >>=20 >> just to be clear: the version of BBR currently implemented is >> BBR version 1, which is known to be unfair in certain scenarios. >> Google is still working on BBR to address this problem and improve >> it in other aspects. But there is no RFC yet and the updates haven't >> been implemented yet in FreeBSD. >=20 > I've also heard that RACK suffers from fairness problems. Do you know > how RACK and BBR compare for fairness? RACK should be fare, BBR (version 1) is known not be be fair... Best regards Michael