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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 10:40:17 +0100


> > And the bulk of that is loading the kernel from fw_cfg.
> Yes after further investigation that is correct.  It looks like
> fw_cfg has grown a DMA interface, but it's not used on x86.
> There is still a considerable amount of SeaBIOS overhead.  In
> particular, it scans the whole of the PCI bus looking for boot
> devices, but that work is both slow and completely unnecessary if
> we're using the linuxbios option ROM to boot.

There have been some experiments to strip down seabios config to speed
up things.

At least on q35 we also might consider using mmconfig, which I think
will reduce the number of vmexits needed for pci config space access.

Oh, and there also is qboot from paolo, but I think this is more a
proof-of-concept thing to see where the limit is.


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