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[173.67.157.122]) by smtp.gmail.com with ESMTPSA id q17sm6179834qtc.19.2018.12.15.21.32.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 15 Dec 2018 21:32:11 -0800 (PST) From: Matt Garber Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\)) Subject: HEADS UP: TCP CUBIC Broken on 12.0-RELEASE/STABLE Message-Id: Date: Sun, 16 Dec 2018 00:32:10 -0500 To: freebsd-stable@freebsd.org X-Mailer: Apple Mail (2.3445.102.3) X-Rspamd-Queue-Id: A0BE77149B X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=eh0RxhV2; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of mattgarber@gmail.com designates 2607:f8b0:4864:20::82f as permitted sender) smtp.mailfrom=mattgarber@gmail.com X-Spamd-Result: default: False [-5.81 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; MV_CASE(0.50)[]; TO_DN_NONE(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; DKIM_TRACE(0.00)[gmail.com:+]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; MX_GOOD(-0.01)[cached: alt3.gmail-smtp-in.l.google.com]; NEURAL_HAM_SHORT(-0.97)[-0.972,0]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_LAST(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; TAGGED_FROM(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com.dwl.dnswl.org : 127.0.5.0]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; MID_RHS_MATCH_FROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-stable@freebsd.org]; RCPT_COUNT_ONE(0.00)[1]; IP_SCORE(-2.33)[ip: (-8.62), ipnet: 2607:f8b0::/32(-1.61), asn: 15169(-1.32), country: US(-0.08)]; RCVD_IN_DNSWL_NONE(0.00)[f.2.8.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0] X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 16 Dec 2018 05:32:13 -0000 Hi all: Just a heads-up for those beginning to test or use FreeBSD 12.0-RELEASE = or 12/STABLE, the alternate TCP congestion control algorithm CUBIC = (cc_cubic) is currently broken and causes complete stalls of certain = network traffic (e.g., rsync, git checkouts, etc.), as well as what = appears to be erratic behavior even for basic SSH. I first noticed on a Digital Ocean VM upgraded from 11.2-RELEASE, but = was then able to consistently reproduce on a fresh 12.0-RELEASE AWS EC2 = instance merely by loading and enabling cc_cubic instead of the default = CC, newreno. H-TCP (cc_htcp) was also tested, but the problem is = isolated to CUBIC. After some discussion on Twitter with Colin Percival, Hiren Panchasara, = and others (thank you!), it was determined that the culprit was r331567 = which hadn=E2=80=99t been reverted prior to 12.0-RELEASE. For those with = custom kernels, reverting that revision in 12/STABLE will fix the = problem with cc_cubic (sys/netinet/cc/cc.h, sys/netinet/cc/cc_cubic.c, = sys/netinet/cc/cc_cubic.h); for those running GENERIC 12.0-RELEASE = kernels, the only immediate workaround is to use newreno or cc_htcp in = the meantime. Hiren has already reverted in HEAD (r342127), and an = Errata Notice will hopefully be published at some point in January after = the holidays. Hope this saves some troubleshooting! =E2=80=94 Thanks, -Matt Garber