Date: Tue, 03 Jan 2017 18:33:26 +0100 From: Harry Schmalzbauer <freebsd@omnilan.de> To: freebsd-virtualization@freebsd.org Subject: Re: Jumbo frames truncated at 4084 bytes by virtio-net? (using if_bridge(4) and vtnet(4) with mtu 9000) Message-ID: <586BE066.7030901@omnilan.de> In-Reply-To: <585AB07C.6010604@omnilan.de> References: <585AA902.50907@omnilan.de> <585AB07C.6010604@omnilan.de>
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Bezüglich Harry Schmalzbauer's Nachricht vom 21.12.2016 17:40 (localtime): > Bezüglich Harry Schmalzbauer's Nachricht vom 21.12.2016 17:08 (localtime): > > … >> Guest flow: >> 16:57:06.642073 00:a0:98:73:9f:42 > 96:07:e9:78:c6:ac, ethertype IPv4 >> (0x0800), length 4085: 172.21.35.1 > 172.21.35.32: ICMP echo request, id >> 27401, seq 0, length 4051 >> 16:57:06.642233 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4 >> (0x0800), length 4084: truncated-ip - 1 bytes missing! 172.21.35.32 > >> 172.21.35.1: ICMP echo reply, id 27401, seq 0, length 405 >> >> Now my problem is that I can't simply keep guest's mtu at 1500, since >> the host will send jumbo frames as answer wich never get through virtio-net. >> >> Does anybody have an idea how to fix/work arround? > For the records, replacing virtio-net with e1000 (as bhyve > PCI-slot-resident) solves the jumbo frame issue! > It seems 82545EM is fully emulated (not 82545GM which doesn't support > jumbo frames) :-) > > Thank you very much for this nice work! > > mav's commit (r302504) mentions heavy performance penalties (factor 2). Real world usage shows slightly heavier penalty. Simply doing 'make package-depends-list' of x11/kde4 takes 1:22 with virtio-net and 3:25 with e1000 (nfsv4 mounted ports tree). I've filed a bug report: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=215737 Hopefully fixing that isn't too complicated... thanks, -harry
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