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Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers
Date: Thu, 31 Mar 2011 23:26:28 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

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<address@hidden>  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.


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