From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Re: VT-X processors , xen 3.0 , drives and virtualization (in 32 bit environment) Date: Tue, 27 Dec 2005 20:07:36 -0600 Message-ID: <43B1F368.1060205@us.ibm.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Brown Cc: Charles Duffy , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Ian Brown wrote: >Hello, > Ok, Thnks,this clears a lot about the first question. > >Still, I will be grateful if I get any feedback on the second question >: performance overhead of running more than one Linux OS instance on >these VT-processors : >did anybody tried it and can comment on it / give some data / compare to >non VT processors >(which have aboutb 3% performance overhead) ? I would expect that >somebody had tried using these >VT chips (even they are still (maybe) in beta stage ). > > VT support in Xen 3.0 is still mostly proof-of-concept. It's not really fair to use it to analyze the performance of VT since there hasn't been a lot (although there has been some) performance work done on VT. The Xen VT support takes a pretty bad performance hit because of the fact that the device model is run in a different domain so there's a pretty big hit from world/context switches. Stay tuned though, because there's no reason why future versions of Xen shouldn't perform quite well under VT :-) Regards, Anthony Liguori >Regards, >IB > > >On 12/27/05, Charles Duffy wrote: > > >>Ian Brown wrote: >> >> >>> 1) True to now and the current xen-3.0 version: When running Xen 3.0 >>> on these VT processors, can we run an unmodified kernel ? >>> >>> >>For your DomUs, yes. For your Dom0, no. Running a modified DomU kernel >>should be more performant. >> >> >> >>> and in such a case, what about the device drivers - isn't there a >>> problem with them ? >>> >>> >>Emulated hardware, based off of drivers borrowed from QEMU, is provided >>to VMX domains. The drivers they need will be for the emulated cards, >>not for the real devices in the machine. >> >> >> >>>I mean , in practical terms , if I will set my bootloader to have the >>>following entry on a machine with VT-x processor: >>> kernel /xen.gz dom0_mem=x >>> module /vmlinuz-#version ro root=... >>> (and initrd if needed) >>> >>> >>No, that won't work, because that's trying to use an unmodified kernel >>as Dom0. >> >> >> >>>will I be >>>able to create a new domain based also on unmodified vmlinuz-#version >>>kernel ? >>> >>> >>Yes, though VMX domains work a bit differently from non-VMX ones -- the >>process won't be exactly the same except with a non-Xen-enabled kernel. >> >> >>_______________________________________________ >>Xen-devel mailing list >>Xen-devel@lists.xensource.com >>http://lists.xensource.com/xen-devel >> >> >> > >_______________________________________________ >Xen-devel mailing list >Xen-devel@lists.xensource.com >http://lists.xensource.com/xen-devel > > >