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Re: [Xen-users] 10gig in domU Simon Hobson Thu Apr 12 01:01:16 2012

Kristoffer Harthing Egefelt wrote:
Using 10G interfaces on kernel 3.2 + xen 4.1.2 we're seeing:
dom0 ~9.2Gbps
domU *~2.5Gbps*

dmesg on domU:
XENBUS: Device with no driver: device/vif/0

Is this normal?

I'm guessing so. I see those messages on every guest when I boot them, then a short time later there are messages relating to drivers/devices. Eg :
[    0.500122] XENBUS: Device with no driver: device/vbd/51713
[    0.500130] XENBUS: Device with no driver: device/vbd/51714
[    0.500137] XENBUS: Device with no driver: device/vbd/51715
[    0.500146] XENBUS: Device with no driver: device/vif/0
[    0.500153] XENBUS: Device with no driver: device/vif/1
[    0.500160] XENBUS: Device with no driver: device/console/0
...
[    0.575270] Initialising Xen virtual ethernet driver.
[    0.669515] blkfront: xvda1: barrier: enabled
[    0.672064] Setting capacity to 4194304
[    0.672089] xvda1: detected capacity change from 0 to 2147483648
[    0.673131] blkfront: xvda2: barrier: enabled
[    0.676030] Setting capacity to 4194304
[    0.676056] xvda2: detected capacity change from 0 to 2147483648
[    0.678393] blkfront: xvda3: barrier: enabled
[    0.700179] Setting capacity to 1048576


As to performance, that has always been a weakness with Xen. AIUI, all the virtual network traffic is handled by a single thread in Dom0 and this creates a bottleneck. There is certainly a huge performance difference between accessing an iSCSI volume natively on the client (poor) vs accessing it on Dom0 and passing it through as a virtual block device (good).

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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