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Date: Tue, 03 Aug 2010 23:20:04 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with
	Linux 2.6.35?
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Gleb Natapov <gleb@redhat.com>, "Richard W.M. Jones" <rjones@redhat.com>

   Hi,

>> We're already doing bulk data transfer over fw_cfg as we need to do it
>> to transfer roms and potentially a boot splash.
>
> Why do we need to transfer roms? These are devices on the memory bus or
> pci bus, it just needs to be there at the right address.

Indeed.  We do that in most cases.  The exceptions are:

   (1) -M somethingold.  PCI devices don't have a pci rom bar then by
       default because they didn't not have one in older qemu versions,
       so we need some other way to pass the option rom to seabios.
   (2) vgabios.bin.  vgabios needs patches to make loading via pci rom
       bar work (vgabios-cirrus.bin works fine already).  I have patches
       in the queue to do that.
   (3) roms not associated with a PCI device:  multiboot, extboot,
       -option-rom command line switch, vgabios for -M isapc.

The default configuration (qemu $diskimage) loads two roms: 
vgabios-cirrus.bin and e1000.bin.  Both are loaded via pci rom bar and 
not via fw_cfg.

cheers,
   Gerd