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Re: [Qemu-devel] Why is SeaBIOS used with -kernel?

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] Why is SeaBIOS used with -kernel?
Date: Mon, 21 Mar 2016 08:58:27 +0100

On Sa, 2016-03-19 at 20:31 +0000, Richard W.M. Jones wrote:
> I've been analyzing the libguestfs appliance[1] boot time.  See
> attached file, especially the end of it.
> About 50% of the boot time is because of SeaBIOS.

And the bulk of that is loading the kernel from fw_cfg.

> I'm using the qemu -kernel option.  I understand that the kernel needs
> some BIOS features, eg. video stuff, E820.  But kvmtool comes with a
> really minimal BIOS that implements a tiny number of calls[2] and is
> far faster than SeaBIOS.
> Is there something I'm missing, or for Linux + -kernel could we use a
> much simpler BIOS?

marc (cc'ed) worked on porting the linuxboot option rom over to use the
new fwcfg dma interface, which should make things a order of magnitude
faster.  That seems to be stalled though.  Marc?


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