From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=51999 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q5PU0-0004Od-CS for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:32:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q5PTz-0002tl-9w for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:32:48 -0400 Received: from mail-yx0-f173.google.com ([209.85.213.173]:47101) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q5PTz-0002tc-6E for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:32:47 -0400 Received: by yxk8 with SMTP id 8so1355302yxk.4 for ; Thu, 31 Mar 2011 14:32:46 -0700 (PDT) Message-ID: <4D94F2FC.4000509@codemonkey.ws> Date: Thu, 31 Mar 2011 16:32:44 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers References: <20110331174328.GA25133@redhat.com> <4D94C916.6080709@codemonkey.ws> <20110331184940.GA25688@redhat.com> <4D94CFA0.3030605@codemonkey.ws> <4D94D62E.2060206@codemonkey.ws> <20110331212628.GA27239@redhat.com> In-Reply-To: <20110331212628.GA27239@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Peter Maydell , Alex Williamson , qemu-devel@nongnu.org On 03/31/2011 04:26 PM, Michael S. Tsirkin wrote: > On Thu, Mar 31, 2011 at 02:29:50PM -0500, Anthony Liguori wrote: >> On 03/31/2011 02:18 PM, Peter Maydell wrote: >>> On 31 March 2011 20:01, Anthony Liguori wrote: >>>> VGA is just another device. It happens to be that we treat VGA device >>>> memory as something that behaves like ram occassionally but that does not >>>> make it RAM. >>> So, to ask a dumb question, what does make something RAM? >> It's a made up concept that we use to make device performance faster. >> >> Basically, RAM should include all of the memory that a reasonable >> device (that we control) would DMA to and has a relatively stable >> mapping. >> >>> My take on RAM is that RAM is just another device; the only >>> difference is that you want to be able to implement fast >>> paths that go straight(ish) to target memory; but that's >>> an optimisation detail, not something that makes RAM >>> conceptually different from other devices... >> Right, the trouble is, if you want to treat RAM like any other >> device, you can't get stable mappings to it which is bad for >> something like vhost-net. >> >> Regards, >> >> Anthony Liguori > Not only that I guess. Removing the VGA memory with the baloon > will likely also be a bad idea. It's just the equivalent of a memset(0). It would be a silly thing for a guest to do but not somethign to be concerned about. Regards, Anthony Liguori