From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54411 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q5PZA-0008E7-BQ for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:38:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q5PZ7-0003nY-KQ for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:38:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47581) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q5PZ7-0003nL-8C for qemu-devel@nongnu.org; Thu, 31 Mar 2011 17:38:05 -0400 Date: Thu, 31 Mar 2011 23:37:43 +0200 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers Message-ID: <20110331213743.GA27264@redhat.com> 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> <4D94F2FC.4000509@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D94F2FC.4000509@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 04:32:44PM -0500, Anthony Liguori wrote: > 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 > BTW, what is IO_MEM_NOTDIRTY? I thought another way would be to replace IO_MEM_RAM with IO_MEM_DEVICE_SHADOW_RAM in these cases but no idea what the right value for that enum would be. -- MST