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

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] Why is SeaBIOS used with -kernel?
Date: Fri, 1 Apr 2016 19:41:31 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Fri, Apr 01, 2016 at 11:35:40AM -0400, Kevin O'Connor wrote:
> > +# general stuff
> Why force a size of 128K - I would think 64K would be fine.

Agreed.  Setting this to =0 seems the best thing, and it does fit fine
inside 64K.

> > +# no input, no boot menu
> [...]
> I would not recommended disabling CONFIG_MOUSE, CONFIG_KEYBOARD,
> CONFIG_DRIVES - I only had those in my config so as to avoid having to
> specify all the device drivers.  Ideally these would remain on and the
> individual device drivers would be disabled.

We are always use this in a virtual appliance.  Interaction with the
user is both impossible and undesirable.  It either boots or not, and
the whole appliance is discarded in seconds.  We're always using
-kernel with this SeaBIOS build, so probing drives is never needed.

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

Result: 1116.0ms ±5.0ms

Result: 1106.6ms ±5.0ms

Result: 1104.7ms ±11.2ms


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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