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

[Richard W.M. Jones]

On Fri, Apr 01, 2016 at 10:58:19AM -0400, Kevin O'Connor wrote:
> On Fri, Apr 01, 2016 at 09:44:56AM +0100, Richard W.M. Jones 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.
> 
> CONFIG_SMBIOS and CONFIG_ACPI only control the legacy internal bios
> tables.  One would disable CONFIG_FW_ROMFILE_LOAD to disable the newer
> ACPI tables; there is no config option currently to disable the newer
> smbios tables.
> 
> These config names are a bit misleading, so they probably should be
> changed in seabios.
> 
> I didn't expect disabling the above options to do anything besides
> reduce the size of the seabios binary, so I'm a bit suprised it saved
> 2ms.  Did you have something on your qemu command-line to avoid
> generating acpi/smbios tables?

The standard deviation of that number over 5 runs was 1ms, so I'm
somewhat confident the 2ms is measuring something real.  In the grand
scheme of things it doesn't matter at all.

I'm not using any qemu command line options related to acpi or smbios.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/