[SeaBIOS] [PATCH v2] qemu: fast boot when linuxboot optionrom is used

Gerd Hoffmann kraxel at redhat.com
Fri Nov 30 14:06:31 CET 2018


> > Note: All these tests are done with CONFIG_DEBUG_LEVEL=0, using
> > CONFIG_DEBUG_LEVEL=1 the boot time grows up to 24 ms, maybe we should
> > put CONFIG_DEBUG_LEVEL=0 in the SeaBIOS configuration used in QEMU.
> I think the main seabios binary should have CONFIG_DEBUG_LEVEL=1 as it
> helps with debug reports.  I suppose an additional binary could be
> made for those looking for the fastest possible speed.  (The sole cost
> of the debugging is the additional hardware accesses that results from
> those debug messages.)

The qemu debugcon (CONFIG_DEBUG_IO) is detecable at runtime, it returns
0xe9 on port reads.  So we should be able to skip that too.  IIRC it
isn't *that* straightforward as seabios is initially mapped read/only so
a simple probe-on-first-putchar, then cache the result in a variable
doesn't work.  We could probe after make_bios_writable though which
should still avoid printing most of the messages.


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