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Comment by pquerna | Hacker News Reader

Intertwined with this announcement of an new instance type, is that it uses a non-Xen hypervisor.

Has anyone booted one yet? Is it KVM or something from scratch that AWS wrote?

It's based on KVM: https://aws.amazon.com/ec2/faqs/#compute-optimized

(sorry for crappy link, can't figure out how to link directly to the appropriate question. Search for "What is the underlying hypervisor on C5 instances" question).

There must be something we can test

Maybe find a new regression

Should we try it on a db shard?

Or exercise some discretion...

instance sizes aren’t powers of two

The discount's just 15 percent

We can hand wave that away

It shouldn’t cause a downtime event

Let’s be adults here I say...

Everything xen, everything xen

I don't think so

Everything xen, everything xen

I don't think so

— Bush, Everything Xen

https://aws.amazon.com/ec2/faqs/#compute-optimized

" Q. What is the underlying hypervisor on C5 instances?

C5 instances use a new EC2 hypervisor that is based on core KVM technology. "

Very interesting. Has anyone noticed any difference in boot times?

If they are announcing things like a brand new hypervisor ahead of re:Invent one wonders what they are saving for the main event...is it too much to hope for managed Kubernetes?

Just did a quick test. It booted up in about 11s vs around 19s for Xen.

I did notice that it took a while for the status check to go green though. There was a warning message saying that it couldn't connect to the instance. I was able to SSH just fine though.

What’s the benefit of KVM over Xen these days?

It's difficult to make an simple comparison because neither hypervisor is used "out of the box" by EC2. For example, a lot of hypervisor benchmark comparisons focus on I/O performance, but the latest generation EC2 instances offload networking and storage processing to hardware. This is the case for both for instances that use Xen and C5 that uses the new KVM-based hypervisor.

Since both hypervisors have very good support for hardware virtualization technology, it becomes more of an architecture decision. Practically speaking, it is a little bit easier to build a very small footprint hypervisor with the core KVM code than Xen.

I am also curious. I found this article which might help a little bit: https://www.theregister.co.uk/2017/01/30/google_cloud_kicked...

KVM can take better advantage of hardware acceleration than Xen. Xen requires a modified guest, which traps back to the host more frequently.

Is that true with the newer modes? https://wiki.xen.org/wiki/Understanding_the_Virtualization_S...

This is based on a cursory examination of [1], so I may be off-base. But Xen appears to rely on the host for many things that can be, and often are, hardware accelerated in KVM. Searching for CONFIG_XEN_PVHVM, it doesn't appear to cover much.

[1] https://github.com/torvalds/linux/blob/master/arch/x86/xen/

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