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Re: [Qemu-devel] [RFC 0/9] Introduce light weight PC platform pc-lite

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] [RFC 0/9] Introduce light weight PC platform pc-lite
Date: Thu, 23 Jun 2016 13:55:06 +0100
User-agent: Mutt/1.6.1 (2016-04-27)

On Mon, Jun 20, 2016 at 02:12:17PM +0800, Chao Peng wrote:
> On Sun, Jun 19, 2016 at 06:51:04AM +0300, Michael S. Tsirkin wrote:
> > On Fri, Jun 17, 2016 at 04:14:08AM -0400, Chao Peng wrote:
> > > - it is FAST;
> > 
> > Any numbers to demonstrate just how fast it is and fast at what?
> On a 2.30GHz Haswell server, guest kernel booting time is 59.9ms by
> following test steps listed at
> https://github.com/chao-p/qemu-lite-tools
> Ran the same test with "-machine q35", the guest kernel booting
> time is 129.8ms. There is additional 75ms in SeaBIOS for Q35 case.

I think it'd be useful / interesting to understand why we have saved
this time vs Q35. I'm not a huge fan of the idea of defining an
arbitrarily cut down machine type, because inevitably one applications
view of what is the "bare minimum required functionality" will be
different from another applications' view.

It seems to me that whether some features emulated by QEMU are slow
or not should only matter if the guest OS actually tries to use those
features. IOW, could we achieve the same speed up in boot time, by
making Linux more configurable at runtime. eg so with a single Linux
kernel binary and standard Q35/PIIX machine type, we can disable
slow functionality by just giving Linux suitable kernel command
line arguments.

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