From owner-freebsd-xen@freebsd.org Wed Mar 17 08:23:50 2021 Return-Path: Delivered-To: freebsd-xen@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 7750857E949 for ; Wed, 17 Mar 2021 08:23:50 +0000 (UTC) (envelope-from buhrow@nfbcal.org) Received: from nfbcal.org (ns.NFBCAL.ORG [157.22.230.125]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "nfbcal.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4F0jq93FHcz4rMt for ; Wed, 17 Mar 2021 08:23:49 +0000 (UTC) (envelope-from buhrow@nfbcal.org) Received: from nfbcal.org (localhost [127.0.0.1]) by nfbcal.org (8.15.2/8.14.1-NFBNETBSD) with ESMTPS id 12H8NkGe024755 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 17 Mar 2021 01:23:47 -0700 (PDT) Received: (from buhrow@localhost) by nfbcal.org (8.15.2/8.12.11) id 12H8Nkuo014508; Wed, 17 Mar 2021 01:23:46 -0700 (PDT) Message-Id: <202103170823.12H8Nkuo014508@nfbcal.org> From: Brian Buhrow Date: Wed, 17 Mar 2021 01:23:46 -0700 X-Mailer: Mail User's Shell (7.2.6 beta(4.pl1)+dynamic 20000103) To: freebsd-xen@freebsd.org Subject: Issue with packet framing on xnb(4) connections and NetBSD domus X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.4.3 (nfbcal.org [127.0.0.1]); Wed, 17 Mar 2021 01:23:47 -0700 (PDT) X-Rspamd-Queue-Id: 4F0jq93FHcz4rMt X-Spamd-Bar: --- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=pass (mx1.freebsd.org: domain of buhrow@nfbcal.org designates 157.22.230.125 as permitted sender) smtp.mailfrom=buhrow@nfbcal.org X-Spamd-Result: default: False [-3.20 / 15.00]; ARC_NA(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[157.22.230.125:from]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; R_SPF_ALLOW(-0.20)[+a:ns.nfbcal.org:c]; MID_RHS_MATCH_FROM(0.00)[]; MIME_GOOD(-0.10)[text/plain]; TO_DN_NONE(0.00)[]; DMARC_NA(0.00)[nfbcal.org]; SPAMHAUS_ZRD(0.00)[157.22.230.125:from:127.0.2.255]; TO_MATCH_ENVRCPT_SOME(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_HAM_SHORT(-0.90)[-0.900]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:7091, ipnet:157.22.0.0/16, country:US]; RCVD_COUNT_TWO(0.00)[2]; MAILMAN_DEST(0.00)[freebsd-xen] X-BeenThere: freebsd-xen@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Discussion of the freebsd port to xen - implementation and usage List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 17 Mar 2021 08:23:50 -0000 hello. I've noticed that on my Xen server, running FreeBSD-12.2/Xen-4.14.0, I see a lot of messages like the following from my NetBSD-5 and NetBSD-current domu's: xennet0: discarding oversize frame (len=1518) They happen when network traffic is heavy and when traffic is coming from a physical switch in the same vlan as the domu's. Since I don't think packets are actually oversized on the wire, the Cisco switch managing this network does not report any giant packets, I think this is a software problem either on the NetBSD domu's, or the FreeBSD dom0. Since I've been running these same NetBSD domu setups on a machine where NetBSD is the dom0, I think this is an issue with the xnb(4) or netback.c driver. Specifically, it looks like it concatinates multiple packets together before notifying the domu that there is traffic available. Perhaps that is by design, since I cannot reproduce the issue on a FreeBSD-domu running on the same FreeBSD-dom0 machine. In either case, while things are usable, it creates a very noisy log on the NetBSD-domu machines. Does the xnb(4) driver forward multiple packets to the domu front ends and set the length of the message to the sum of the lengths of all the packets it's forwarding, leaving it to the domu front end driver to separate the packets on reception? Is there a parameter that can be set on a per-domu basis to say whether you want multiple-packets-per-transfer or not from the dom0? -thanks -Brian