Xen users - Apr 2006 - PAE performance cost on an Dual Opteron 265 with 8GB of RAM

Hi,

I have a dual 265 with 8GB of RAM. I was planning on putting the 64
bit build of Xen on it but a friend of mine is a bit of a NetBSD bunny
and so I am considering putting the 32 bit build on as NetBSD doesn''t
work on Opteron/64 bits.

As far as I''m aware to access all 8GB of memory I''ll need to
enable
PAE on xen? Is this correct?

None of the DomU''s will have more than 1GB of RAM (probably none will
have that much - most likely 512MB max). Am I right in thinking that
all the Linux kernels will need PAE turned on? I get that impression
from http://lists.xensource.com/archives/html/xen-users/2005-11/msg00442.html

There is a performance overhead with PAE isn''t there? What kind of hit
am I looking at? Is it something to be worried about? >10% ?  I know
that question is moderately unanswerable in a strong sense but a feel
would be really handy.

Thanks guys
-Rob

--
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"Which exclusive club are: My mother, my ex, and Patricia Measham a
member of? They''re all people who have spanked me!" -Rob
"But those enemies of mine who did not want me to be king over
them—bring them here and kill them in front of me." - Jesus (Luke
19:27)

http://www.robhulme.com/
http://robhu.livejournal.com/

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On Tuesday 18 April 2006 05:37, Robert Hulme wrote:
> As far as I''m aware to access all 8GB of memory I''ll need
to enable
> PAE on xen? Is this correct?
Isn''t PAE just for the 32-bit systems to allow them to access up to
64GB?  I
believe the Opteron can access 1TB natively.

John


-- 
John Madden
Sr. UNIX Systems Engineer
Ivy Tech Community College of Indiana
jmadden@ivytech.edu

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> On Tuesday 18 April 2006 05:37, Robert Hulme wrote:
> > As far as I''m aware to access all 8GB of memory I''ll
need to enable
> > PAE on xen? Is this correct?
> Isn''t PAE just for the 32-bit systems to allow them to access up
to 64GB?  I
> believe the Opteron can access 1TB natively.
Err yes. I don''t think I was clear enough.

With 64 bit Xen it doesn''t need PAE to access all the RAM but my
question is about using a 32 bit Xen kernel (which would need PAE)
rather than a 64 bit kernel as NetBSD is not compatible with 64 bit
AMD64 kernels yet.

I can use a 32 bit kernel with PAE on my Opteron as it is capable of
running normal x86 code (presumably which also includes PAE).

-Rob
--
------------------------------------------------------
"Women are always right when they''re /naked/" - Andrew Neil
"But those enemies of mine who did not want me to be king over
them—bring them here and kill them in front of me." - Jesus (Luke
19:27)

http://www.robhulme.com/
http://robhu.livejournal.com/

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