[Bug 215471] Using bsnmpd with the snmp_hostres module on a vmware ESXi guest with a disconnected CD drive uses 100% CPU

[bugzilla-noreply]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=215471

Mark Linimon  changed:

   What|Removed |Added

   Assignee|freebsd-b...@freebsd.org|freebsd-virtualization@Free
   ||BSD.org
 CC|freebsd-am...@freebsd.org   |

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Re: Jumbo frames truncated at 4084 bytes by virtio-net? (using if_bridge(4) and vtnet(4) with mtu 9000)

[Harry Schmalzbauer]

 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).
Has anyone tried the influence of disabling/keeping offload functions in
the guest?

Thanks,

-Harry
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Jumbo frames truncated at 4084 bytes by virtio-net? (using if_bridge(4) and vtnet(4) with mtu 9000)

[Harry Schmalzbauer]

 Hello,

I'm having guest connectivity problems with jumbo frames.

Since if_bridge(4) requires all interfaces to have the same MTU (and the
uplink interface also handles iscsi traffic, which greatly benefits from
jumbo frames), I
'ifconfig create vmnet0 mtu 9000'

Afert adding it to the bridge 'ifconfig bregn addm vmnet0' and setting
guest mtu to 9000 (which vtnet(4) claims to support), I can transceive
frames larger than 1500,
which this flow from the guest's vtnet(4) interface demonstrates:
16:54:36.672709 00:a0:98:73:9f:42 > 96:07:e9:78:c6:ac, ethertype IPv4
(0x0800), length 4084: 172.21.35.1 > 172.21.35.32: ICMP echo request, id
56840, seq 0, length 4050
16:54:36.672791 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4
(0x0800), length 4084: 172.21.35.32 > 172.21.35.1: ICMP echo reply, id
56840, seq 0, length 4050
On the host this looks similar.

Now with a payload size of 4043 instead of 4042 bytes, the reply never
makes it through virtio-net:
Host flow:
16:57:06.641382 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
16:57:06.641399 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4
(0x0800), length 4085: 172.21.35.32 > 172.21.35.1: ICMP echo reply, id
27401, seq 0, length 4051
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?

Thanks,

-harry
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