linux-kernel - Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (aka NPT-Virtualization)

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Date:	Thu, 4 Mar 2010 00:44:48 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (aka NPT-Virtualization)


On 03.03.2010, at 20:12, Joerg Roedel wrote:

> Hi,
> 
> here are the patches that implement nested paging support for nested
> svm. They are somewhat intrusive to the soft-mmu so I post them as RFC
> in the first round to get feedback about the general direction of the
> changes.  Nevertheless I am proud to report that with these patches the
> famous kernel-compile benchmark runs only 4% slower in the l2 guest as
> in the l1 guest when l2 is single-processor. With SMP guests the
> situation is very different. The more vcpus the guest has the more is
> the performance drop from l1 to l2. 
> Anyway, this post is to get feedback about the overall concept of these
> patches.  Please review and give feedback :-)

Nice job! It's great to see you finally got around to it :-).

Have you tracked what slows down SMP l2 guests yet? So far I've been assuming that IPIs just completely kill the performance, but I guess it shouldn't be that bad, especially now where you have sped up the #VMEXIT path that much.


Alex--
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