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

[Kevin O'Connor]

On Wed, Nov 28, 2018 at 12:30:42PM +0100, Stefano Garzarella wrote:
> On Wed, Nov 28, 2018 at 3:12 AM Kevin O'Connor <kevin at koconnor.net> wrote:
> > On Mon, Nov 26, 2018 at 12:39:12PM +0100, Stefano Garzarella wrote:
> > > Speed up the boot phase when qemu uses "linuxboot" optionrom
> > > (qemu -kernel) and the boot-menu is not required.
> > > Under these conditions we can skip the setup of devices and VGA,
> > > because they will be initialized (if they are required) during
> > > the Linux boot phase.
> > >
> > > Following the time measured between SeaBIOS entry point and
> > > "linuxboot" entry point:
> > >
> > > * Before this patch
> > >   qemu -kernel  | qemu -vga none -kernel
> > >   --------------+-----------------------
> > >   53.5 msec     | 23.34 msec
> > >
> > > * After this patch
> > >   qemu -kernel  | qemu -vga none -kernel
> > >   --------------+-----------------------
> > >   12.82 msec    | 10.89 msec
> > >
> > > Note: For the measuring, we used the default configuration disabling
> > > debug messages (CONFIG_DEBUG_LEVEL=0) and applying Stephen's patch:
> > > "tpm: Check for TPM related ACPI tables before attempting hw"
> > >
> > > Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
> > > ---
> > >  src/bootsplash.c  |  3 +++
> > >  src/fw/paravirt.c | 10 ++++++++++
> > >  src/fw/paravirt.h |  4 ++++
> > >  src/optionroms.c  |  3 ++-
> > >  src/post.c        |  3 +++
> > >  5 files changed, 22 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/src/bootsplash.c b/src/bootsplash.c
> > > index 165c98d..0eda7f2 100644
> > > --- a/src/bootsplash.c
> > > +++ b/src/bootsplash.c
> > > @@ -8,6 +8,7 @@
> > >  #include "bregs.h" // struct bregs
> > >  #include "config.h" // CONFIG_*
> > >  #include "farptr.h" // FLATPTR_TO_SEG
> > > +#include "fw/paravirt.h" // runningOnQEMUFastBoot
> > >  #include "malloc.h" // free
> > >  #include "output.h" // dprintf
> > >  #include "romfile.h" // romfile_loadfile
> > > @@ -39,6 +40,8 @@ call16_int10(struct bregs *br)
> > >  void
> > >  enable_vga_console(void)
> > >  {
> > > +    if(runningOnQEMUFastBoot())
> > > +        return;
> > >      dprintf(1, "Turning on vga text mode console\n");
> > >      struct bregs br;
> > >
> > > diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
> > > index 0770c47..9e6e618 100644
> > > --- a/src/fw/paravirt.c
> > > +++ b/src/fw/paravirt.c
> > > @@ -621,4 +621,14 @@ void qemu_cfg_init(void)
> > >      if (nogfx && !romfile_find("etc/sercon-port")
> > >          && !romfile_find("vgaroms/sgabios.bin"))
> > >          const_romfile_add_int("etc/sercon-port", PORT_SERIAL1);
> > > +
> > > +    /*
> > > +     * Enable QEMU fast boot if there is "linuxboot" optionrom and
> > > +     * the boot menu is not required.
> > > +     */
> > > +    if ((romfile_find("genroms/linuxboot_dma.bin")
> > > +        || romfile_find("genroms/linuxboot.bin"))
> > > +        && !romfile_loadint("etc/show-boot-menu", 1)) {
> > > +        PlatformRunningOn |= PF_QEMU_FB;
> > > +    }
> >
> > I don't think we should hardcode special meanings to the names of
> > bootable files.  If QEMU wants SeaBIOS to not perform some type of
> > hardware init, then I think QEMU should explicitly request that from
> > SeaBIOS (eg, a "etc/dont-run-hardware-init").
> 
> I agree, it is cleaner. That was one of my doubt but, with an explicit
> request, it works only with a new version of QEMU.
> Do you think is acceptable?

It would be good to understand what the source of the delay is.  It
might be possible to avoid the delay without adding a new config
setting.  For example, the patch above will prevent the vga rom from
being run, but it should be possible to accomplish the same with
"-device VGA,romfile=".  The other change this patch makes is to skip
device_hardware_setup() - is it known which items in that function add
to the delay?

Also, what is the target boot time that is considered acceptable?

Thanks,
-Kevin