From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/6] Add rudimentary Hyper-V guest support Date: Mon, 18 May 2009 16:29:49 +0300 Message-ID: <4A1162CD.4060900@redhat.com> References: <1242375740-31222-1-git-send-email-agraf@suse.de> <0EF5ED01-F027-470C-B766-3DB8EF616AE8@suse.de> <4A107CE1.2030707@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: KVM list , Joerg Roedel To: Alexander Graf Return-path: Received: from mx2.redhat.com ([66.187.237.31]:41837 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905AbZERN3y (ORCPT ); Mon, 18 May 2009 09:29:54 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Alexander Graf wrote: >> >> There's only a limited potential here (a factor of three, reducing 6 >> exits to 2, less the emulation overhead). There's a lot more to be >> gained from nested npt, since you'll avoid most of the original exits >> in the first place. > > I think the reversed is the case. Look at those numbers (w2k8 bootup): > > http://pastebin.ca/1423596 > > The only thing nested NPT would achieve is a reduction of #NPF exits. > But they are absolutely in the minority today already. Normal #PF's do > get directly passed to the guest already. #NPF exits are caused when guest/host mappings change, which they don't, or by mmio (which happens both for guest and nguest). I don't understand how you can pass #PFs directly to the guest. Surely the guest has enabled pagefault interception, and you need to set up its vmcb? > > Of course, this all depends on the workload. For kernbench style > benchmarks nested NPT probably gives you a bigger win, but anything > doing IO is slowed down way more than it has to now. What is causing 17K pio exits/sec? What port numbers? -- error compiling committee.c: too many arguments to function