From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pat Campbell Subject: Re: Re: userspace block backend / gntdev problems Date: Sun, 27 Jan 2008 17:40:03 -0700 Message-ID: <479D2463.8060509@novell.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 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: Keir Fraser Cc: Derek Murray , Xen Development Mailing List , Markus Armbruster , Gerd Hoffmann List-Id: xen-devel@lists.xenproject.org Keir Fraser wrote: > On 26/1/08 08:41, "Markus Armbruster" wrote: > > >>> In my latest post on "Dynamic modes support for PV xenfb" I am using >>> grants to map an extended framebuffer. I have a single grant ref that >>> points to 10 other refs. The other refs contain MFNs. Same technique as >>> the current framebuffer pd array but avoids the 64bit long issue. Kind >>> of a hybrid approach. I am able to map a 22MB framebuffer when running a >>> 64 bit guest and 44MB when running a 32 bit guest. When the backend is >>> done with the mapping it sends a message to the frontend to free up the >>> refs. >>> >> Uhm, I fear I didn't get the advantage of your hybrid approach. Could >> you explain? >> > > Presumably it allows creation of huge framebuffers without using up lots of > grants, or slots in accounting tables that Xen maintains. Given that those > tables can dynamically grow, I'm not sure how useful the two-level grant > table would be. > > -- Keir > > > Well, turns out my email did not really get sent. Keir is right, it is a two level grant table. Solution might not be useful in the general case but for this device I think it fits the bill. Existing xenfb code is already doing a two level table which has to be maintained for backward compatibility reasons, might as well be consistent. Also by using a two level grant table we don't have to extend the event structure which might be a compatibility issue. I will get my patches sent up for your review directly. Pat