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Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?
Date: Wed, 4 Aug 2010 14:24:08 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Wed, Aug 04, 2010 at 08:15:04AM -0500, Anthony Liguori wrote:
> On 08/04/2010 08:07 AM, Gleb Natapov wrote:
> >On Wed, Aug 04, 2010 at 08:04:09AM -0500, Anthony Liguori wrote:
> >>On 08/04/2010 03:17 AM, Avi Kivity wrote:
> >>>For playing games, there are three options:
> >>>- existing fwcfg
> >>>- fwcfg+dma
> >>>- put roms in 4GB-2MB (or whatever we decide the flash size is)
> >>>and have the BIOS copy them
> >>>
> >>>Existing fwcfg is the least amount of work and probably
> >>>satisfactory for isapc.  fwcfg+dma is IMO going off a tangent.
> >>>High memory flash is the most hardware-like solution, pretty easy
> >>>from a qemu point of view but requires more work.
> >>
> >>The only trouble I see is that high memory isn't always available.
> >>If it's a 32-bit PC and you've exhausted RAM space, then you're only
> >>left with the PCI hole and it's not clear to me if you can really
> >>pull out 100mb of space there as an option ROM without breaking
> >>something.
> >>
> >We can map it on demand. Guest tells qemu to map rom "A" to address X by
> >writing into some io port. Guest copies rom. Guest tells qemu to unmap
> >it. Better then DMA interface IMHO.
> That's what I thought too, but in a 32-bit guest using ~3.5GB of
> RAM, where can you safely get 100MB of memory to full map the ROM?
> If you're going to map chunks at a time, you are basically doing
> DMA.

It's boot time, so you can just map it over some existing RAM surely?
Linuxboot.bin can work out where to map it so it won't be in any
memory either being used or the target for the copy.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
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