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[Xen-devel] Re: [RFC, PATCH 1/24] i386 Vmi documentation II

To: Zachary Amsden <zach@xxxxxxxxxx>
Subject: [Xen-devel] Re: [RFC, PATCH 1/24] i386 Vmi documentation II
From: Andi Kleen <ak@xxxxxxx>
Date: Thu, 23 Mar 2006 00:37:58 +0100
Cc: Andrew Morton <akpm@xxxxxxxx>, Joshua LeVasseur <jtl@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Pratap Subrahmanyam <pratap@xxxxxxxxxx>, Wim Coekaerts <wim.coekaerts@xxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxx>, Jack Lo <jlo@xxxxxxxxxx>, Dan Hecht <dhecht@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, Christopher Li <chrisl@xxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Linus Torvalds <torvalds@xxxxxxxx>, Anne Holler <anne@xxxxxxxxxx>, Jyothy Reddy <jreddy@xxxxxxxxxx>, Kip Macy <kmacy@xxxxxxxxxxx>, Ky Srinivasan <ksrinivasan@xxxxxxxxxx>, Leendert van Doorn <leendert@xxxxxxxxxxxxxx>, Dan Arai <arai@xxxxxxxxxx>
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On Thursday 23 March 2006 00:54, Zachary Amsden wrote:
> Andi Kleen wrote:
> > On Wednesday 22 March 2006 23:45, Zachary Amsden wrote:
> >
> >   
> >> I propose an entirely different approach - use segmentation. 
> >>     
> >
> > That would require a lot of changes to save/restore the segmentation
> > register at kernel entry/exit since there is no swapgs on i386. 
> > And will be likely slower there too and also even slow down the 
> > VMI-kernel-no-hypervisor.
> >   
> 
> There are no changes required to the kernel entry / exit paths.  With 
> save/restore segment support in the VMI, reserving one segment for the 
> hypervisor data area is easy.

Ok that might work yes.

> > Still might be the best option.
> >
> > How did that rumoured Xenolinux-over-VMI implementation solve that problem?
> >   
> 
> !CONFIG_SMP  -- as I believe I saw in the latest Xen patches sent out as 
> well?

Ah, cheating. This means the rumoured benchmark numbers are dubious too I guess.

-Andi

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