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[Xen-devel] Re: iommu=1 by default?

To: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: iommu=1 by default?
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 19 Jan 2010 10:09:57 +0000
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On 19/01/2010 09:59, "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx> wrote:

> Would it make sense to make "iommu=1" the default for xen 4.0?
> 
> I think Xen is rather more defensive these days about disabling iommu in the
> presence of broken BIOS tables, but there may conceivably still be machines it
> breaks boot on. I can't think of any subtle bugs the IOMMU could introduce if
> it's not explicitly in use by VMs -- and I don't believe anyone has seen any
> performance issues. [We could actually not fully turn the IOMMU on until the
> first VM that demands it.]
> 
> Would it make sense to turn it on by default in the release candidates? Or too
> late? 
> 
> IOMMU is clearly going to be a widely used feature in this release.

We could enable by default in -rc2 and then disable for final release if
there are bug reports that are not fixable in time.

 -- Keir




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