Re: [Xen-users] 32bit or 64bit dom0?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Jan 26, 2010 at 08:30:40AM -0800, Grant McWilliams wrote:
>    On Tue, Jan 26, 2010 at 7:31 AM, Pasi KÃârkkÃâinen <[1]pasik@xxxxxx>
>    wrote:
> 
>      On Tue, Jan 26, 2010 at 06:22:38PM +0700, Fajar A. Nugraha wrote:
>      > On Tue, Jan 26, 2010 at 3:06 PM, Ian Tobin <[2]itobin@xxxxxxxxxxxxx>
>      wrote:
>      > > Thanks for the info guys, ive been playing with 3.4.2 on 32bits but
>      im thinking for the future it would be worth having 64bits for things
>      like win2008R2 as this is 64 bit only.
>      >
>      > If Windows is your only concern, IIRC 32bit xen can run 64bit HVM
>      > domUs just fine. What does "xm info" say about caps?
>      >
> 
>      I think you need 64b Xen hypervisor to run 64b guests,
>      but dom0 Linux can be still 32bit PAE.
>      > Personally I use 64bit xen, dom0, and domU so it would be easier when
>      > I need to assign one of them with memory over 4GB, since using 32bit
>      > PAE has some performance penalty.
>      >
> 
>      I think there was some benchmarks about this recently and the
>      PAE performance hit wasn't very big..
> 
>      Anyway, it's better to use 64b nowadays.
>      -- Pasi
> 
>    That depends one whether you consider (up to) 20% worth considering! I'd
>    be willing to change for 5%.
> 
>    [3]http://www.phoronix.com/scan.php?page=article&item=616&num=1
> 

Hmm.. did you paste wrong url? That url only has 32b vs. 64b?

Here's 32b vs. 32b PAE benchmark:
http://www.phoronix.com/scan.php?page=article&item=ubuntu_32_pae

Although that benchmark must have something wrong with the 32 vs 64 numbers.. 
the different can't be THAT big.

"In the fourteen tests for this article we did not find using Ubuntu's 32-bit 
PAE kernel 
to have a dramatic performance impact whether it be positive or negative. 

Granted, we were using just 4GB of system memory that is common to many 
desktops, 
but if using 8GB, 16GB, or even a greater memory capacity the performance 
penalties are perhaps higher. "

-- Pasi


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