qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [RFC v4 00/58] Memory API


From: Sasha Levin
Subject: Re: [Qemu-devel] [RFC v4 00/58] Memory API
Date: Wed, 20 Jul 2011 09:10:51 +0300

On Tue, 2011-07-19 at 21:53 -0500, Anthony Liguori wrote:
> QEMU does use it and it's quite important.  Coalesced MMIO is really 
> about write caching MMIO exits.  It only works with devices that have 
> registers where writing has no side effects.  Moreover, it only really 
> works well when there are lots and lots of writes to these registers 
> simultaneously.
> 
> Couple that with the fact that the buffer is a fixed size and it's 
> really not flexible enough to be useful for a wide variety of devices.
> 
> But for VGA planar mode writes, it works wonders.  It would be terrible 
> to totally lose it.  That said, I'm not at all convinced it's useful for 
> much other than VGA planar mode.

Why was the coalesced approach taken in the first place? When I tried
using it for VGA in /tools/kvm it just seemed to me like a builtin
virtio-memory transport.

Thats why I think planar VGA would be fine if we deprecate coalesced
mmio in favor of either socket ioeventfds or a new virtio-memory device.

-- 

Sasha.




reply via email to

[Prev in Thread] Current Thread [Next in Thread]