qemu: Move from pc-lite to pc machine type

[sboeuf]

This patch modifies the default configuration provided through the
Makefile so that our runtime will use "pc" machine type for our
Qemu hypervisor. This change implies that we have to use vmlinuz
which is the compressed kernel expected by the BIOS run by "pc"
machine type.

Fixes #329

[coveralls]

Coverage remained the same at 55.39% when pulling 8a38fa7 on sboeuf/move_to_pc into 7c7832d on master.

[wcwxyz]

Is there any story behind this? Why are you choosing pc over q35 or pc-lite?

[sboeuf]

Hi @wcwxyz, the story behind this is that we want to be able to hotplug devices to our VM after it has been started, meaning that we need this functionality from qemu. The q35 machine type is the evolution of our qemu-lite current machine type, but unfortunately the hotplug feature of PCI devices is not working.
We made some run some PnP tests and we agreed they were okay so that we can move to the "pc" machine type.

[wcwxyz]

Thanks @sboeuf. I understand.

I see there's some not upstream'd patches in https://github.com/clearcontainers/qemu/commits/qemu-lite-v2.9.0 to fix/improve q35 and pc-lite.

I mean pc must be a trade-off comparing to the other two. Do you have benchmark of pc/pc-lite/q35 regarding memory footprint/boot time or other performance aspect? How much performance we will lose by switching to pc?

[sboeuf]

@wcwxyz We have some PnP metrics but this is not something that we can share externally unless we get some approvals from Intel.

[wcwxyz]

That's ok. I believe PnP is quite fast.

But what about memory footprint and VM boot time?

[sboeuf]

@wcwxyz what we call PnP (Power and Performance) gathers all the metrics, meaning that boot time and memory footprint are parts of what we cannot share externally.

[wcwxyz]

@sboeuf I see. I thought it's Plug and Play, the hot plug stuff. Thanks for answering my question.

[sboeuf]

@wcwxyz Sure no problem ;)

[jodh-intel]

lgtm