Xen users - Jul 2006 - xenU / xen0 - or a single (xen) kernel?

from the README:

" These are smaller builds with just selected
   modules, intended primarilly for developers that don''t like to wait
   for a -xen kernel to build. The -xenU kernel is particularly small
   as it does not contain any physical device drivers, and hence is
   only useful for guest domains."

correct me here, but does that mean for a typical rollout you want to
just build the xen kernel, and not the xenU/xen0 ??

reason I ask, is that it seems to be the standard practice to build
both, but that isnt quite what I interpret from the notes.

If anyone can point to or summarize some performance benefits for
either route, that would be great.

Thanks


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> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Chris McKeever
> Sent: 26 July 2006 01:28
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] xenU / xen0 - or a single (xen) kernel?
> 
> from the README:
> 
> " These are smaller builds with just selected
>    modules, intended primarilly for developers that don''t like to
wait
>    for a -xen kernel to build. The -xenU kernel is particularly small
>    as it does not contain any physical device drivers, and hence is
>    only useful for guest domains."
> 
> correct me here, but does that mean for a typical rollout you want to
> just build the xen kernel, and not the xenU/xen0 ??
> 
> reason I ask, is that it seems to be the standard practice to build
> both, but that isnt quite what I interpret from the notes.
> 
> If anyone can point to or summarize some performance benefits for
> either route, that would be great.
It works just fine to do either (one or two kernels). There shouldn''t
be
any performance difference between the two. The main reason, as stated
above, to have two kernels is that you can reduce the size of the XenU
kernel because it doesn''t need all the drivers for real hardware. But
if
you''re using initrd, it won''t make a whole lot of difference,
since the
modules for real devices won''t be loaded in DomU anyway, as the devices
never appear in the "plug&play" phase... 

The only reason you''d get some performance difference would be if the
smaller kernel fits in the cache a little bit better - but since kernel
functions themselves would be the same whether you have no, some or many
drivers, each kernel call will not take any more or less space in the
cache, so that leaves the fact that the kernel calls are at different
places - which will be randomly good or bad for the application anyways,
so no better or worse...

Just building one seems like a fine idea to me... 

[I don''t run much para-virtual, as my work is to develop the HVM
version
of Xen, and thus don''t really run Para-virtual kernel]. 

--
Mats
> 
> Thanks
> 
> 
> -- 
> ----------------------------------
> please respond to the list .. if you need to contact me direct
> cgmckeever is the account
> prupref.com is the domain
> 
> <A href="http://www.prupref.com">Simply Chicago Real
Estate</A>
> 
> _______________________________________________
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