Re: [Xen-devel] Xen 4.3: x86 32 bit code removed or depreciated?

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 10/07/13 12:32, George Dunlap wrote:
> On Wed, Jul 10, 2013 at 12:28 PM, Ian Murray <murrayie@xxxxxxxxxxx> wrote:
> 
>>> Just to be clear, this is the 32-bit *hypervisor* which was removed.
>>> 32-bit tools in a 32-bit dom0 still work.
>>>
>>
>> Thanks. Thanks for clearing that up. Perhaps off-topic for dev, but are 
>> there any advantages to running a 32 bit dom0 as in this configuration?
> 
> Probably the biggest thing is about performance.  Until the PVH mode
> is implemented, 64-bit PV guests will have a performance degradation,
> due to the way the architecture changed between 32-bit and 64-bit.

This isn't really that true for real dom0 workloads.

Most of the theoretical performance penalty caused by system calls
having to trap into the hypervisor are offset by the general performance
improvement of the amd64 archiecture (e.g., more general purpose
registers and the lack of high memory needing bouncing/mapping all the
time).

David

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