[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
Hi,
> > 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.
cheers,
Gerd
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