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

[Kevin O'Connor]

On Fri, Apr 01, 2016 at 07:59:02PM +0100, Richard W.M. Jones wrote:
> On Fri, Apr 01, 2016 at 07:41:31PM +0100, Richard W.M. Jones wrote:
> > Below are some benchmarks of the other things you mentioned.  These
> > are complete appliance boot-to-shutdown times [*not* just SeaBIOS].
> > All debugging has been disabled, and I'm using a slightly different
> > kernel version, so these runs are not comparable to earlier results I
> > posted.  All times are the mean of 10 runs.  The ± number is 1
> > standard deviation from the mean.
> > 
> > In my estimation only CONFIG_FW_ROMFILE_LOAD=n seems to make a
> > measurable difference.
> > 
> > ----------------------------------------------------------------------
> > Ordinary qemu SeaBIOS configuration
> > Result: 1227.5ms ±7.7ms
> > 
> > -bios boot-fast.bin, as per my previous patch
> > Result: 1113.7ms ±6.4ms
> > 
> > Leaving CONFIG_XEN and CONFIG_THREADS at default settings
> > Result: 1111.2ms ±3.8ms
> > 
> > CONFIG_USE_SMM=n
> > Result: 1116.0ms ±5.0ms
> > 
> > CONFIG_FW_ROMFILE_LOAD=n
> > Result: 1106.6ms ±5.0ms
> > 
> > CONFIG_RELOCATE_INIT=n
> > Result: 1104.7ms ±11.2ms
> > ----------------------------------------------------------------------
> 
> Actually, CONFIG_RELOCATE_INIT=n looks like it is doing something, but
> the error bars are quite large.
> 
> Here's another one that makes a difference:
> 
> CONFIG_BOOTORDER=n
> Result: 1099.5ms ±3.7ms

Are you sure you had CONFIG_DEBUG_LEVEL=0?  Otherwise, it doesn't make
sense that disabling CONFIG_BOOTORDER=n would change the boot time.
Disabling CONFIG_DEBUG_SERIAL is not enough, because SeaBIOS also
writes to port 0x402 as an internal debugging mechanism.

-Kevin