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

["Richard W.M. Jones" <rjones@redhat.com>]

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On Fri, Apr 01, 2016 at 01:32:51PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > I think we were working on the same thing ...  Attached is my
> > version.
> > 
> > Note that you must enable at least CONFIG_MPTABLE else virtio-scsi
> > does not work in the guest.  I also enabled ACPI & SMBIOS & PIRTABLE.
> 
> They are enabled by default, no need to explicitly say so ;)

So they are.  Here's a v3 patch.

I also retested everything from scratch.  Previously I was testing the
stock SeaBIOS bios.bin shipped with qemu vs the fast config.  However
that has the possible problem that I was testing two slightly
different versions of SeaBIOS (whatever version qemu ships vs
upstream).

Testing from scratch, using upstream SeaBIOS in both cases, there's
still a significant benefit.  SeaBIOS overhead goes from 63 ms down to
19 ms (saving 44 ms).

Overall the proportion of boot time of the libguestfs appliance
attributed to SeaBIOS drops from 3.7% to 1.1% (but note this is with
libguestfs & kernel debugging enabled -- for real users there'd be a
much larger percentage drop).

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

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>From 8cdf91f13949ab46c6a5804b968400d404c4e00e Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Fri, 1 Apr 2016 11:35:09 +0100
Subject: [PATCH] bios: Add fast variant of SeaBIOS for use with -kernel on
 x86.

This commit adds a fast variant of SeaBIOS called 'bios-fast.bin'.

It's designed to be the fastest (also the smallest, but that's not the
main aim) SeaBIOS that is just enough to boot a Linux kernel using the
-kernel option on i686 and x86_64.

This commit does not modify the -kernel option to use this.  You have
to specify it by doing something like this:

  -kernel vmlinuz -bios bios-fast.bin

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 Makefile                 |  3 ++-
 roms/Makefile            |  4 +++-
 roms/config.seabios-fast | 25 +++++++++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 roms/config.seabios-fast

diff --git a/Makefile b/Makefile
index 1d076a9..c4e939d 100644
--- a/Makefile
+++ b/Makefile
@@ -389,7 +389,8 @@ common  de-ch  es     fo  fr-ca  hu     ja  mk  nl-be      pt  sl     tr \
 bepo    cz
 
 ifdef INSTALL_BLOBS
-BLOBS=bios.bin bios-256k.bin sgabios.bin vgabios.bin vgabios-cirrus.bin \
+BLOBS=bios.bin bios-256k.bin bios-fast.bin \
+sgabios.bin vgabios.bin vgabios-cirrus.bin \
 vgabios-stdvga.bin vgabios-vmware.bin vgabios-qxl.bin vgabios-virtio.bin \
 acpi-dsdt.aml \
 ppc_rom.bin openbios-sparc32 openbios-sparc64 openbios-ppc QEMU,tcx.bin QEMU,cgthree.bin \
diff --git a/roms/Makefile b/roms/Makefile
index 7bd1252..26b0586 100644
--- a/roms/Makefile
+++ b/roms/Makefile
@@ -61,9 +61,11 @@ default:
 	@echo "  slof           -- update slof.bin"
 	@echo "  u-boot.e500    -- update u-boot.e500"
 
-bios: build-seabios-config-seabios-128k build-seabios-config-seabios-256k
+bios: build-seabios-config-seabios-128k build-seabios-config-seabios-256k \
+      build-seabios-config-seabios-fast
 	cp seabios/builds/seabios-128k/bios.bin ../pc-bios/bios.bin
 	cp seabios/builds/seabios-256k/bios.bin ../pc-bios/bios-256k.bin
+	cp seabios/builds/seabios-fast/bios.bin ../pc-bios/bios-fast.bin
 
 seavgabios: $(patsubst %,seavgabios-%,$(vgabios_variants))
 
diff --git a/roms/config.seabios-fast b/roms/config.seabios-fast
new file mode 100644
index 0000000..f035b49
--- /dev/null
+++ b/roms/config.seabios-fast
@@ -0,0 +1,25 @@
+# The fastest SeaBIOS that can boot Linux using -kernel.
+
+# general stuff
+CONFIG_QEMU=y
+CONFIG_ROM_SIZE=128
+CONFIG_XEN=n
+CONFIG_THREADS=n
+CONFIG_WRITABLE_UPPERMEMORY=y
+
+# no input, no boot menu
+CONFIG_MOUSE=n
+CONFIG_KEYBOARD=n
+CONFIG_BOOTMENU=n
+CONFIG_BOOTSPLASH=n
+
+# hardware support we don't need
+CONFIG_LPT=n
+CONFIG_SERIAL=n
+CONFIG_USB=n
+CONFIG_DRIVES=n
+CONFIG_TCGBIOS=n
+CONFIG_VGAHOOKS=n
+
+# no logging
+CONFIG_DEBUG_LEVEL=0
-- 
2.7.4