Re: [PATCH v9 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

Maran Wilson
2018-12-12T21:57:14Z

On 12/12/2018 12:39 PM, Borislav Petkov wrote:
> On Tue, Dec 11, 2018 at 11:29:21AM -0800, Maran Wilson wrote:
>> Is your question about what options you need to provide to Qemu? Or is your
>> question about the SW implementation choices?
>>
>> Assuming the former...
> Yeah, that's what I wanted to know. But looking at it, I'm booting
> bzImage here just as quickly and as flexible so I don't see the
> advantage of this new method for my use case here of booting kernels
> in qemu.
>
> But maybe there's a good use case where firmware is slow and one doesn't
> really wanna noodle through it or when one does start a gazillion VMs
> per second or whatever...

Right, the time saved is not something you would notice while starting a
VM manually. But it does reduce the time to reach startup_64() in Linux
by about 50% (going from around 94ms to around 47ms) when booting a VM
using Qemu+qboot (for example). That time savings becomes pretty
important when you are trying to use VMs as containers (for instance, as
is the case with Kata containers) and trying to get the latency for
launching such a container really low -- to come as close as possible to
match the latency for launching more traditional containers that don't
have the additional security/isolation of running within a separate VM.

Thanks,
-Maran

>
> Thx.
>