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Re: [Xen-devel] Re: lazy context switching

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Subject: Re: [Xen-devel] Re: lazy context switching
From: Hollis Blanchard <hollisb@xxxxxxxxxx>
Date: Tue, 30 Aug 2005 11:22:48 -0500
Cc: Dan Magenheimer <dan.magenheimer@xxxxxx>
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On Tuesday 30 August 2005 10:25, Dan Magenheimer wrote:
> Sorry for the late reply... keeping up with xen-devel
> is getting tough!

Yes, I just occasionally skim...

> How does Linux do this on Power?  Xen/ia64 heavily
> leverages the equivalent Linux/ia64 code.  As you
> may know, Linux/ia64 scatters state all over
> memory and uses "unwind descriptors" so that it
> can recover all the state.  I'd imagine Power does
> something similar...

Linux has a per-kernel thread stack, so '_switch' saves the current (i.e. 
kernel, not original usermode) nonvolatiles to the previous task structure.

For Xen/PPC, we use a per-cpu stack, so we need to save the original (domain) 
nonvolatiles to the previous domain structure.

Hollis Blanchard
IBM Linux Technology Center

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