From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: Paravirtualization on VMware's Platform [VMI]. Date: Tue, 22 Sep 2009 20:02:16 +0200 Message-ID: <20090922180216.GA16789@elte.hu> References: <1253233028.19731.63.camel@ank32.eng.vmware.com> <20090919224430.GB9567@kroah.com> <1253419185.3253.21.camel@ank32.eng.vmware.com> <20090920074247.GA5733@elte.hu> <20090920095239.456ad6f2@infradead.org> <4AB5EF25.9070502@redhat.com> <4AB64EFC.10707@goop.org> <20090922080913.GB1475@elte.hu> <4AB900CC.7090409@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4AB900CC.7090409@goop.org> Sender: linux-kernel-owner@vger.kernel.org To: Jeremy Fitzhardinge Cc: Avi Kivity , Arjan van de Ven , Alok Kataria , Thomas Gleixner , "H. Peter Anvin" , the arch/x86 maintainers , LKML , Chris Wright , Rusty Russell , "virtualization@lists.osdl.org" , Greg KH , Linus Torvalds , Andrew Morton List-Id: virtualization@lists.linuxfoundation.org * Jeremy Fitzhardinge wrote: > On 09/22/09 01:09, Ingo Molnar wrote: > >>> kvm will be removing the pvmmu support soon; and Xen is talking about > >>> running paravirtualized guests in a vmx/svm container where they don't > >>> need most of the hooks. > >>> > >> We have no plans to drop support for non-vmx/svm capable processors, > >> let alone require ept/npt. > > > > But, just to map out our plans for the future, do you concur with > > the statements and numbers offered here by the VMware and KVM folks > > that on sufficiently recent hardware, hardware-assisted > > virtualization outperforms paravirt_ops in many (most?) workloads? > > Well, what Avi is referring to here is some discussions about a hybrid > paravirtualized mode, in which Xen runs a normal Xen PV guest within a > hardware container in order to get some immediate optimisations, and > allow further optimisations like using hardware assisted paging > extensions. > > For KVM and VMI, which always use a shadow pagetable scheme, hardware > paging is now unambigiously better than shadow pagetables, but for Xen > PV guests the picture is mixed since they don't use shadow pagetables. > The NPT/EPT extensions make updating the pagetable more efficent, but > actual access is more expensive because of the higher load on the TLB > and the increased expense of a TLB miss, so the actual performance > effects are very workload dependent. obviously they are workload dependent - that's why numbers were posted in this thread with various workloads. Do you concur with those conclusions that they are generally a speedup over paravirt? If not, which are the workloads where paravirt offers significant speedup over hardware acceleration? Ingo