Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?

[Gleb Natapov <gleb@redhat.com>]

On Wed, Aug 04, 2010 at 11:44:33AM -0500, Anthony Liguori wrote:
> On 08/04/2010 11:36 AM, Avi Kivity wrote:
> > On 08/04/2010 07:30 PM, Avi Kivity wrote:
> >> On 08/04/2010 04:52 PM, Anthony Liguori wrote:
> >>>>>
> >>>>This is not like DMA event if done in chunks and chunks can be pretty
> >>>>big. The code that dials with copying may temporary unmap some pci
> >>>>devices to have more space there.
> >>>
> >>>
> >>>That's a bit complicated because SeaBIOS is managing the PCI
> >>>devices whereas the kernel code is running as an option rom.
> >>>I don't know the BIOS PCI interfaces well so I don't know how
> >>>doable this is.
> >>>
> >>>Maybe we're just being too fancy here.
> >>>
> >>>We could rewrite -kernel/-append/-initrd to just generate a
> >>>floppy image in RAM, and just boot from floppy.
> >>
> >>How could this work?  the RAM belongs to SeaBIOS immediately
> >>after reset, it would just scribble over it.  Or worse, not
> >>scribble on it until some date in the future.
> >>
> >>-kernel data has to find its way to memory after the bios gives
> >>control to some optionrom.  An alternative would be to embed
> >>knowledge of -kernel in seabios, but I don't think it's a good
> >>one.
> >>
> >
> >Oh, you meant host RAM, not guest RAM.  Disregard.
> >
> >This is basically my suggestion to libguestfs: instead of
> >generating an initrd, generate a bootable cdrom, and boot from
> >that.  The result is faster and has a smaller memory footprint.
> >Everyone wins.
> 
> Yeah, but we could also do that entirely in QEMU.  If that's what we
> suggest doing, there's no reason not to do it instead of the option
> rom trickery that we do today.
> 
> The option rom stuff has a number of short comings.  Because we
> hijack int19, extboot doesn't get to run.  That means that if you
> use -kernel to load a grub (the Ubuntu guys for their own absurd
> reasons) then grub does not see extboot backed disks.  The solution
> for them is the same, generate a proper disk and boot from that
> disk.
> 
Extboot is not so relevant any more.

--
			Gleb.