Re: [Qemu-devel] Why is SeaBIOS used with -kernel?

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Richard W.M. Jones (rjones@redhat.com) wrote:
> On Fri, Apr 01, 2016 at 10:24:37AM +0200, Paolo Bonzini wrote:
> > On 01/04/2016 10:14, Richard W.M. Jones wrote:
> > > Found it: only CONFIG_MPTABLE=y was necessary.  It boots with:
> > > 
> > > # CONFIG_PIRTABLE is not set
> > > CONFIG_MPTABLE=y
> > > # CONFIG_SMBIOS is not set
> > > # CONFIG_ACPI is not set
> > 
> > If you add all three it should not give any slowdown and will provide
> > full hardware features to the kernel.  qboot does ACPI and PCI bus
> > assignment (it doesn't do SMBIOS because I got bored debugging it. :))
> 
> Enabling all 4 adds about 2ms.
> 
> However the overhead of SeaBIOS is still down from 68ms to 18ms
> (4.0% of total boot time down to 1.1%) so it's still a big gain.
> 
> I wonder how we can make use of this in qemu and downstream distros?
> Can we have a bios-min.bin which is used with -kernel boots?

Could we pass a flag at runtime that gets the standard image to skip a lot
of the stuff you don't want?

Or is there anything else qemu could provide (e.g. a fast way to get
to PCI config space?)

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK