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From: Bill Huey (hui) <billh@gnuppy.monkey.org>
Subject: Re: VKernel progress update - 9 Jan 2006
Date: Thu, 11 Jan 2007 18:05:53 -0800
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References: <20070111024457.55cc5a7e.bastyaelvtars@gmail.com> <49195.192.168.0.252.1168489103.squirrel@www.shiningsilence.com> <200701111859.l0BIxdDQ094385@apollo.backplane.com> <20070111231614.GA30442@gnuppy.monkey.org> <200701120041.l0C0fYDK097057@apollo.backplane.com> <20070112005155.GA31215@gnuppy.monkey.org> <20070112005352.GA31560@gnuppy.monkey.org> <200701120121.l0C1LQdI097380@apollo.backplane.com> <20070112013508.GA32061@gnuppy.monkey.org> <200701120153.l0C1rubl097624@apollo.backplane.c
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On Thu, Jan 11, 2007 at 05:53:56PM -0800, Matthew Dillon wrote:
[MMU fault, modification and loading issues]
. .. 
>     I don't have numbers for page table faults, but at least for those
>     the real kernel doesn't have to drop into the virtual kernel unless
>     the emualted page table is missing the page table entry for the VA.
>     (the real kernel handles setting the VPTE_M bit itself).  I still have
>     some work to do there today and tomorrow that might improve performance
>     a bit.

VMWare, I believe, actually does a partial binary translation of MMU
instructions and higher order operations into direct kernel calls that
can modify the host image directly. I guess that helps out with context
switching performance, but this is a chronic problem for all Xen-ish
systems that I know of that doesn't have a really transparent solution.

bill