[SeaBIOS] [Qemu-devel] SeaBIOS booting time optimization

[Stefano Garzarella]

On Thu, Nov 22, 2018 at 12:51 PM Gerd Hoffmann <kraxel at redhat.com> wrote:
>
> On Thu, Nov 22, 2018 at 12:08:55PM +0100, Stefano Garzarella wrote:
> > Hi,
> > I continued to investigate how to reduce the boot time with SeaBIOS
> > and QEMU when it used with linuxboot_dma.bin (-kernel parameter).
> > I reached ~12ms with a SeaBIOS configuration (attached) where I
> > disabled debug output, all Hardware support (except SMM & MTRRs) and I
> > applied a small patch to disable VGA setup and console (attached).
>
> Is there any difference to "qemu -vga none" ?

Using both (qemu -vga none, and my patch) we are around 10.8 ms.
Note: using only the patch, Linux is still able to initialize and use the VGA.

- QEMU -vga none + SeaBIOS config (CONFIG_DEBUG_LEVEL=0, disable all
HW support except
SMM & MTRRs) + Stephen's TPM patch
 qemu_init_end: 43.675803
 fw_start: 43.865178 (+0.189375)
 fw_do_boot: 58.093161 (+14.227983)
 linux_start_boot: 59.490308 (+1.397147)
 linux_start_user: 556.782354 (+497.292046)

- QEMU -vga none + SeaBIOS config (CONFIG_DEBUG_LEVEL=0, disable all
HW support except
SMM & MTRRs, CONFIG_DISABLE_VGA=y) + Stephen's TPM patch
 qemu_init_end: 42.387412
 fw_start: 42.579257 (+0.191845)
 fw_do_boot: 53.381517 (+10.802260)
 linux_start_boot: 54.848643 (+1.467126)
 linux_start_user: 498.517050 (+443.668407)

>
> > Samuel, I put also the total time to userspace (linux_start_user)
> > adding a probe in the kernel_init() and when I disabled the VGA in the
> > SeaBIOS I noticed also a speed up in the kernel boot phase.
>
> Might come from linux 16bit boot code scanning vgabios for available
> video modes (for vga=<mode> cmdline arg).
>
> > Another approach that I tried, obtaining similar results, is to
> > recognize the linuxboot_dma.bin at runtime, then skip
> > device_hardware_setup(), enable_vga_console(), and vgarom_setup().
>
> Hmm, tricky.
>"
> linuxboot_dma.bin just registers a boot entry, so with "qemu -kernel
> -boot menu=on" you can still get a boot menu, and the direkt kernel boot
> is one menu item there.  So you can't know for sure whenever a direct
> kernel boot will happen or not.
>
> So, I think at minimum we should make this depend on both linuxboot_dma
> and boot menu disabled.

You are right! I'll prepare a patch adding the check of boot menu.

Thanks,
Stefano

>
> cheers,
>   Gerd
>


--
Stefano Garzarella
Red Hat