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

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Jan 26, 2010 at 02:01:53PM -0600, Steven Wilcoxon wrote:
>    Many people also forget about the performance boost on CPU intensive apps
>    by running 64 bit mode, even if you don't need extra memory. This can be a
>    5%-15% depending on the application. This includes the OS. The reason is
>    64 bit mode not only allows 64 bit memory access and registers, but it
>    also doubles the number of registers available.
> 
>    I would always recommend to use 64 bit whenever possible unless there is a
>    pressing need to stick with 32 bit.
> 

64b apps use more memory than the same app on 32b.. and executables are bigger.
But yeah, ram and disk are so cheap nowadays that 64b is the way to go.

-- Pasi

>    S.W.
> 
>    On 1/26/2010 11:05 AM, Grant McWilliams wrote:
> 
>      On Tue, Jan 26, 2010 at 8:45 AM, Pasi KÃrkkÃinen <[1]pasik@xxxxxx>
>      wrote:
> 
>        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][2]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][3]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][4]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:
>        [5]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
> 
>      Yes I did! Thanks. Here try this.
> 
>      [6]http://www.phoronix.com/scan.php?page=article&item=ubuntu_32_pae&num=1
> 
>      Grant McWilliams
> 
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