[DC LoCo] Testing 12.04 LTS development branch on system with IOMMU and SR-IOV

[Ken Stailey]

In case you were wondering, a simple explanation of what SR-IOV accomplishes is that it allows a single network card to appear as several network cards.

A separate technology "PCI pass-through" allows a virtual machine to access a physical PCI card directly.  In the case of a PCI network card it is much faster for a virtual machine to use a physical network card than to emulate one in software. 


If you know what an MMU is and what a south bridge is, you can think of the IOMMU as an MMU for the south bridge.  The IOMMU takes care of doing the memory remapping required to allow a virtual machine to directly access the PCI card.

By combining SR-IOV and PCI pass-though several virtual machines can directly access the same physical network card.  Otherwise you would need a VM host with a large number of network cards.



________________________________
From: Ken Stailey <kstailey at yahoo.com>
To: DC Ubuntu <Ubuntu-us-dc at lists.ubuntu.com> 
Sent: Friday, January 13, 2012 6:16 PM
Subject: Re: [DC LoCo] Testing 12.04 LTS development branch on system with IOMMU and SR-IOV



After a day of work the system is running 12.04 but SR-IOV is not working.

https://bugs.launchpad.net/bugs/790201

But Red Hat supposedly supports it and there are spare disks in the system that can be used to bring up CentOS 6.2 to see if it is true or not.  If it works there it is definitely worth testing Yinghai Lu's manual-overide patches (see https://bugs.launchpad.net/ubuntu/+source/linux/+bug/790201/comments/9 for links to those patches.)