From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: paravirtual drivers? Date: Thu, 12 Apr 2007 12:42:10 -0500 Message-ID: <461E6F72.2040805@us.ibm.com> References: <461DFE2E.3020805@wpkg.org> <64F9B87B6B770947A9F8391472E032160B4A9CF0@ehost011-8.exch011.intermedia.net> <1176381086.3844.4.camel@laptopd505.fenrus.org> <64F9B87B6B770947A9F8391472E032160B4A9D60@ehost011-8.exch011.intermedia.net> <1176389824.3417.0.camel@laptopd505.fenrus.org> <461E4AAF.8050606@codemonkey.ws> <1176394563.3417.7.camel@laptopd505.fenrus.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Arjan van de Ven Return-path: In-Reply-To: <1176394563.3417.7.camel-NIQFrBLA1CpScpXdPBN83iCwEArCW2h5@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 Arjan van de Ven wrote: > On Thu, 2007-04-12 at 10:05 -0500, Anthony Liguori wrote: > >> Why not drive the backend from userspace? >> > > (nothing in the concept requires it to be in the kernel, it just makes > things a lot easier) > > Because I think the trend forward is to reduce the userspace dependency > of kvm, not increase it. There's no increase in dependency since block IO is already done in userspace. Besides, I think the general Linux trend of moving things to userspace when there's no compelling reason to have them in kernel space trumps all other trends ;-) > And because you add context switches etc etc > There's no context switch just a privilege transition. Granted, privilege transitions aren't free but they're aren't that much compared to the cost of processing an IO request. >> Are you using a ring queue to >> transmit bio's from the guest to the host? >> > > sort of; it's not quite a real ring (I'm using the block layer tagged > queueing which is more efficient than a ring actually) > I'm not sure I understand. I guess I can just read the code. What I was wondering was whether you put the bio's into a shared ring queue or whether you issued a hypercall per bio. >> What are you using for >> discovery (I assume PCI)? >> > > I just added a hypercall to enumerate. Adding a dummy PCI is probably > needed for OS installers to auto-load the drivers. > Ah, okay. >> Could you post a copy of your driver on the list? I think it would be >> good to discuss. >> > > I'll dig it up > Excellent. Thank you! Regards, Anthony Liguori ------------------------------------------------------------------------- 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