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

From: Paolo Bonzini
Subject: Re: [Qemu-devel] Announcing qboot, a minimal x86 firmware for QEMU
Date: Mon, 25 May 2015 14:52:51 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 23/05/2015 01:23, Kevin O'Connor wrote:
> Hi Paolo,
> I'm curious if you've tried profiling SeaBIOS to see where it is
> spending unnecessary time?

No, I really wanted to get the absolute minimum time needed to get to
the kernel.  I announced it publicly because I think it's also instructive.

> I wonder if a stripped down SeaBIOS could
> obtain sufficient performance.

It most likely could.  However, some of the features (e.g. booting
vmlinuz from parallel flash or, in the future, from persistent memory)
probably do not fit SeaBIOS very well.  One would have to redo them
otherwise, for example using a DMA interface in fw_cfg.


> 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
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