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

[Chao Peng]

> 
> I think a lightweight q35 platform that can run the usual firmware could
> be acceptable in QEMU.

After re-thought the target usage model, I'm not sure if this is a good
idea.

The original usage model is to replace kvm-tool with QEMU for Clear
Containers (https://clearlinux.org/features/clear-containers). It's not
going to present the guest a real PC platform, but instead, a totally
virtual platform. Every little bit boot time saving is important because
we are trying to achieve comparable result with that for Linux native
container.

With this usage model, I doubt introducing a firmware layer is a good
idea:

    On one side, even with optimized and compact qboot it still takes us
    ~15ms. This is not a small value because current Linux kernel takes
    only ~50ms (and we are still on the way to optimize it). And when
    you look at the SeaBIOS or qboot, almost all the code are useless for
    this usage model. They are doing things that is important for
    traditional PC booting but cost 15ms doing useless things for us (It
    is really not easy to save 15ms in other place, for example, in
    Linux. Personally I tend to change the architecture for this new
    usage model, e.g. eliminate firmware).

    On the other side, even boot the new pc-lite platform with firmware,
    it does not mean it can support non-Linux system like Windows. So
    generally I don't see the benefit of introducing a firmware layer.

Besides, I'm also not quite sure if build around Q35 is the best
solution:

    The problem with Q35 is some features like SMM/SMRAM/PAM slow done
    the booting even we actually never use them. While removing these
    features can cause guest see different feature set for a same device
    and it also prevents us to do further optimizations on that in guest.

Really appreciate if you could give some more suggestions or other usage
models if you have.

Thanks,
Chao