From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=44221 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Q5NZ5-00063Y-4q
	for qemu-devel@nongnu.org; Thu, 31 Mar 2011 15:29:56 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1Q5NZ3-0007Ed-U2
	for qemu-devel@nongnu.org; Thu, 31 Mar 2011 15:29:55 -0400
Received: from mail-gx0-f173.google.com ([209.85.161.173]:63864)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1Q5NZ3-0007EQ-Rf
	for qemu-devel@nongnu.org; Thu, 31 Mar 2011 15:29:53 -0400
Received: by gxk26 with SMTP id 26so1300696gxk.4
	for <qemu-devel@nongnu.org>; Thu, 31 Mar 2011 12:29:53 -0700 (PDT)
Message-ID: <4D94D62E.2060206@codemonkey.ws>
Date: Thu, 31 Mar 2011 14:29:50 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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>
	<AANLkTi=mfnmrcbezqKZWkns-RiRbBDNyiBpqGBtGO=Jp@mail.gmail.com>
In-Reply-To: <AANLkTi=mfnmrcbezqKZWkns-RiRbBDNyiBpqGBtGO=Jp@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Alex Williamson <alex.williamson@redhat.com>, qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>

On 03/31/2011 02:18 PM, Peter Maydell wrote:
> On 31 March 2011 20:01, Anthony Liguori<anthony@codemonkey.ws>  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

> -- PMM
>