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

[Anthony Liguori <anthony@codemonkey.ws>]

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.

Regards,

Anthony Liguori