On Fri, Apr 01, 2016 at 12:49:47PM +0100, Richard W.M. Jones wrote: > On Fri, Apr 01, 2016 at 01:32:51PM +0200, Gerd Hoffmann wrote: > > > 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
> From 8cdf91f13949ab46c6a5804b968400d404c4e00e Mon Sep 17 00:00:00 2001 > From: "Richard W.M. Jones" <rjo...@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 It's possible to build a third binary, but that seems like it would be a bit annoying for distributions. I think most of the benefit could be obtained by just adding a flag to seabios to have it skip device driver initialization. That's where the majority of the time saved is from. [...] > --- /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 Why force a size of 128K - I would think 64K would be fine. > +CONFIG_XEN=n > +CONFIG_THREADS=n I doubt either of these two would change timing at all. There's no harm in disabling CONFIG_XEN, but I would not recommend disabling CONFIG_THREADS. > +CONFIG_WRITABLE_UPPERMEMORY=y > + > +# no input, no boot menu > +CONFIG_MOUSE=n > +CONFIG_KEYBOARD=n [...] > +CONFIG_DRIVES=n I would not recommended disabling CONFIG_MOUSE, CONFIG_KEYBOARD, CONFIG_DRIVES - I only had those in my config so as to avoid having to specify all the device drivers. Ideally these would remain on and the individual device drivers would be disabled. > +CONFIG_BOOTMENU=n > +CONFIG_BOOTSPLASH=n These two should have no impact on timing at all. > + > +# hardware support we don't need > +CONFIG_LPT=n > +CONFIG_SERIAL=n > +CONFIG_USB=n [...] > +CONFIG_TCGBIOS=n > +CONFIG_VGAHOOKS=n > + > +# no logging > +CONFIG_DEBUG_LEVEL=0 If you really want to go all out on timing tests, you could disable CONFIG_USE_SMM, and CONFIG_FW_ROMFILE_LOAD. Disabling CONFIG_RELOCATE_INIT may help, but probably not. -Kevin
