From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=45775 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q5POF-0001iz-5d for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:26:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q5POE-0001YK-4d for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:26:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55336) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q5POD-0001YE-Qa for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:26:50 -0400 Date: Thu, 31 Mar 2011 23:26:28 +0200 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers Message-ID: <20110331212628.GA27239@redhat.com> References: <20110331174328.GA25133@redhat.com> <4D94C916.6080709@codemonkey.ws> <20110331184940.GA25688@redhat.com> <4D94CFA0.3030605@codemonkey.ws> <4D94D62E.2060206@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D94D62E.2060206@codemonkey.ws> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Peter Maydell , Alex Williamson , qemu-devel@nongnu.org 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. -- MST