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

[Gleb Natapov]

On Wed, Aug 04, 2010 at 11:17:28AM +0300, Avi Kivity wrote:
>  On 08/04/2010 10:56 AM, Gerd Hoffmann wrote:
> >  Hi,
> >
> >>>(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.
> >>
> >>What did we do back then? before we had the fwcfg interface?
> >
> >Have qemu instead of bochs/seabios manage the vgabios/optionrom
> >area (0xc8000 -> 0xe0000) and copy the roms to memory.  Which
> >implies the whole rom has to sit there as PMM can't be used then.
> 
> Do we actually need PMM for isapc?  Did PMM exist before pci?
> 
> >
> >>>(3) roms not associated with a PCI device: multiboot, extboot,
> >>>-option-rom command line switch, vgabios for -M isapc.
> >>
> >>We could lay those out in high memory (4GB-512MB) and have the bios copy
> >>them from there.
> >
> >Yea, we could.  But it is pointless IMHO.
> >
> >$ ls -l *.bin
> >-rwxrwxr-x. 1 kraxel kraxel 1536 Jul 15 15:51 extboot.bin*
> >-rwxrwxr-x. 1 kraxel kraxel 1024 Jul 15 15:51 linuxboot.bin*
> >-rwxrwxr-x. 1 kraxel kraxel 1024 Jul 15 15:51 multiboot.bin*
> >-rwxrwxr-x. 1 kraxel kraxel 8960 Jul 15 15:51 vapic.bin*
> >
> >That are the ones we can't load via pci rom bar.  Look how small
> >they are.
> 
> So they can just sit there?  I'm confused, either there is enough
> address space and we don't need to play games, or there isn't and we
> do.
> 
> 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.
> 
We can do interface like that: guest enumerates available roms using
fwcfg. Guest can tell host to map rom into guest specified IOMEM region.
Guest copies rom from IOMEM region and tell host to unmap it.

--
                        Gleb.