From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: Paravirt KVM capabilities Date: Thu, 11 Jan 2007 11:42:00 +1100 Message-ID: <1168476120.19646.209.camel@localhost.localdomain> References: <20070109141916.GA13276@vlad.carfax.org.uk> <45A3A642.1030604@qumranet.com> <1168384852.19646.161.camel@localhost.localdomain> <20070110094750.GA934@elte.hu> <45A4BB74.9010102@redhat.com> <20070110101839.GA6444@elte.hu> <45A4C345.5050404@qumranet.com> <20070110105202.GA13412@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Return-path: To: Ingo Molnar In-Reply-To: <20070110105202.GA13412-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Wed, 2007-01-10 at 11:52 +0100, Ingo Molnar wrote: > * Avi Kivity wrote: > > > If you have a CONFIG_PARAVIRT guest, I believe it will always be > > faster to run it without hardware assisted virtualization: > > > > - you cannot eliminate vmexits due to host interrupts > > - a hypercall will (probably) keep being more expensive than a syscall; > > it simply has a lot more work to do > > - cr3 switches for CONFIG_PARAVIRT syscalls (which are necessary on > > x86_64) will probably become very cheap with tagged tlbs > > but irq overhead is nothing in importance compared to basic syscall > overhead. KVM/HVM already runs guest kernel syscalls at native speed. > KVM/LL (or Xen) has to switch cr3s to enter guest kernel context Err no, this isn't true. See Documentation/lhype.txt or various blog entries on the subject 8) Both Xen and lhype get native syscall speeds (within measurement error). Rusty. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV