Re: [Qemu-devel] Announcing qboot, a minimal x86 firmware for QEMU

[Kevin O'Connor]

On Thu, May 21, 2015 at 03:51:43PM +0200, Paolo Bonzini wrote:
> Some of you may have heard about the "Clear Containers" initiative from
> Intel, which couple KVM with various kernel tricks to create extremely
> lightweight virtual machines.  The experimental Clear Containers setup
> requires only 18-20 MB to launch a virtual machine, and needs about 60
> ms to boot.
> 
> Now, as all of you probably know, "QEMU is great for running Windows or
> legacy Linux guests, but that flexibility comes at a hefty price. Not
> only does all of the emulation consume memory, it also requires some
> form of low-level firmware in the guest as well. All of this adds quite
> a bit to virtual-machine startup times (500 to 700 milliseconds is not
> unusual)".
> 
> Right?  In fact, it's for this reason that Clear Containers uses kvmtool
> instead of QEMU.
> 
> No, wrong!  In fact, reporting bad performance is pretty much the same
> as throwing down the gauntlet.
> 
> Enter qboot, a minimal x86 firmware that runs on QEMU and, together with
> a slimmed-down QEMU configuration, boots a virtual machine in 40
> milliseconds[2] on an Ivy Bridge Core i7 processor.

Hi Paolo,

I'm curious if you've tried profiling SeaBIOS to see where it is
spending unnecessary time?  I wonder if a stripped down SeaBIOS could
obtain sufficient performance.

The page at http://seabios.org/Debugging#Timing_debug_messages
describes how to do basic profiling via timing of debug messages.

The default SeaBIOS build takes ~180ms on my (old AMD) system.  But,
by removing drivers and options via Kconfig I was able to bring it
down to ~25ms.  I suspect some additional Kconfig settings and a few
optimizations would make it possible to significantly reduce this
time.

Cheers,
-Kevin