Re: [Xen-API] Plans for 64 bit dom0

[James Bulpin <James.Bulpin@xxxxxxxxxxxxx>]

On Tue, May 28, 2013 at 21:28, Pasi wrote:
> On Tue, May 28, 2013 at 01:22:04PM -0500, Phil Ritter wrote:
> >    Are there any plans to deliver a packaged version of XCP (the ISO
> version)
> >    with dom0 built on a 64 bit kernel?
> >    64-bit is becoming more and more important for supporting some new
> device
> >    drivers and storage technology.  Also existing 32 bit dom0 is showing
> its
> >    weakness under heavy I/O workloads.
> >    Debian xcp-xapi is not a good option yet as there are just enough
> >    differences to make it hard to manage.
> >    Perhaps hope for 64-bit in 1.7 release?
> >
> 
> I'm guessing 64bit dom0 will be used in XCP after Xen PVH (hybrid) support
> is merged to
> upstream Xen and upstream Linux kernel, so most probably around Xen 4.4
> timeframe.
> 
> Xen PVH support allows running dom0 in an HVM container.

I suspect it'll take a while for that to stabilise enough for an 
enterprise-class virtualization platform to use it so I wouldn't expect XCP to 
use PVH dom0 for a while after its initial release.

However moving to a 64 bit PV dom0 is a realistic possibility - Citrix 
performance testing has shown that the known 64 bit micro-level slowdown 
(syscalls) doesn't have an appreciable effect on the system-level performance 
for most metrics. There were some notable slowdowns but generally on relatively 
uncommon operations like writing to syslog. The conclusion from the study was 
that moving to a 64 bit PV dom0 would be OK from a performance perspective.

Therefore the current intention is to move XCP to 64 bit PV dom0 later this 
year, at the same time we move to a 3.x kernel. I'm hoping that trunk builds 
(pre-stabilisation) will be available well ahead of full release to give people 
a chance to try them out.

Cheers,
James



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