Re: [Qemu-devel] Slow kernel/initrd loading via fw_cfg; Was Re: Hack integrating SeaBios / LinuxBoot option rom with QEMU trace backends

[Daniel P. Berrange]

On Tue, Oct 11, 2011 at 11:50:01AM +0200, Avi Kivity wrote:
> On 10/11/2011 11:49 AM, Daniel P. Berrange wrote:
> >On Tue, Oct 11, 2011 at 11:39:36AM +0200, Avi Kivity wrote:
> >>  On 10/11/2011 11:27 AM, Daniel P. Berrange wrote:
> >>  >>   >For comparison I also did a test building a bootable ISO using 
> >> ISOLinux.
> >>  >>   >This required 700 ms for the boot time, which is appoximately 1/2 
> >> the
> >>  >>   >time reqiured for direct kernel/initrd boot. But you have to then 
> >> add
> >>  >>   >on time required to build the ISO on every boot, to add custom 
> >> kernel
> >>  >>   >command line args. So while ISO is faster than LinuxBoot currently
> >>  >>   >there is still non-negligable overhead here that I want to avoid.
> >>  >>
> >>  >>   You can accept parameters from virtio-serial or some other channel.
> >>  >>   Is there any reason you need them specifically as *kernel* command
> >>  >>   line parameters?
> >>  >
> >>  >Well some of the parameters are actually kernel parameters :-) The rest
> >>  >are things I pass to the 'init' process which runs in the initrd. When
> >>  >this process first starts the only things it can easily access are those
> >>  >builtin to the kernel image, so data available from /proc or /sys like
> >>  >the /proc/cmdline file. It hasn't even loaded things like the 
> >> virtio-serial
> >>  >or virtio-9pfs kernel modules at this point.
> >>  >
> >>
> >>  It could, if it wanted to.  It's completely custom, yes?
> >
> >I'm thinking primarily about debug related parameters, which need to be
> >used as soon the process starts, not delayed until after we've loaded
> >kernel modules at which point the step we wanted to debug is already
> >past.
> 
> Ah, so there's no issue in regenerating the image if you want to debug.

Compared to just altering the -append arg to QEMU, rebuilding the initrd
image and init program is a PITA.

Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|