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

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers
Date: Thu, 31 Mar 2011 14:29:50 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110223 Lightning/1.0b2 Thunderbird/3.1.8

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.


Anthony Liguori

-- PMM

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