Re: [Qemu-devel] QEMU fw_cfg DMA interface

[Kevin O'Connor]

Trimming CC list.

On Thu, Aug 06, 2015 at 05:53:26PM +0200, Marc Marí wrote:
> On Thu, 6 Aug 2015 11:30:43 -0400
> "Kevin O'Connor" <address@hidden> wrote:
> > On Thu, Aug 06, 2015 at 02:37:45PM +0200, Marc Marí wrote:
> > > On Thu, 6 Aug 2015 13:27:16 +0100
> > > Stefan Hajnoczi <address@hidden> wrote:
> > > 
> > > > On Thu, Aug 6, 2015 at 12:00 PM, Marc Marí <address@hidden>
> > > > wrote:
> > > > > When running a Linux guest on top of QEMU, using the -kernel
> > > > > options, this is the timing improvement for x86:
> > > > >
> > > > > QEMU commit 2be4f242b50a8 and SeaBIOS commit 908a58c1d5ff
> > > > > QEMU startup time: .078
> > > > > BIOS startup time: .060
> > > > > Kernel setup time: .578
> > > > > Total time: .716
> > > > >
> > > > > QEMU with this patch series and SeaBIOS with this patch series
> > > > > QEMU startup time: .080
> > > > > BIOS startup time: .039
> > > > > Kernel setup time: .002
> > > > > Total time: .121
> > > > 
> > > > Impressive results!
> > > > 
> > > > Is this a fully-featured QEMU build or did you disable things?
> > > > 
> > > > Is this the default SeaBIOS build or did you disable things?
> > > > 
> > > 
> > > This is the default QEMU configuration I get for my system. It's
> > > not a fully-featured QEMU, but it has a lot of things enabled.
> > > SeaBIOS has a default configuration (with debugging disabled).
> > 
> > Thanks!
> > 
> > What qemu command-line did you use during testing?  Also, do you have
> > a quick primer on how to use the kvm trace stuff to obtain timings?
> > 
> 
> The command line I used is:
> 
> x86_64-softmmu/qemu-system-x86_64 --enable-kvm \
>     -kernel /boot/vmlinuz-4.0.7-300.fc22.x86_64 \
>     -L pc-bios/optionrom/ \
>     -bios roms/seabios/out/bios.bin -nographic

Thanks.  One thing that immediately pops up is that even though
"-nographic" is used, it looks like QEMU still emulates a VGA device
and that device has an option rom that takes several milliseconds to
init the display hardware.  Adding "-device VGA,romfile=" to the qemu
command line will further reduce the boot time by avoiding this
hardware init delay.

-Kevin