1 vCPU instances do not simultaneously share cores with other customer instances via SMT (Intel Hyper-Threading Technology). A core can be sequentially time sliced between customer instances when you use a fractional (m3.medium) or burst (T2 instances) CPU instance type.

https://aws.amazon.com/ec2/instance-types/ includes a note that provides some additional information about when vCPUs utilize Intel HT Technology: Each vCPU is a hyperthread of an Intel Xeon core except for T2 and m3.medium. (emphasis added)

https://aws.amazon.com/ec2/virtualcores/ provides a table of the number of cores allocated per instance. Notice that an instance like m5.large that has 2 vCPUs and 1 core. An instance like t2.small has 1 vCPU and 1 core.

Disclosure: I work for AWS

Um, no. If I schedule a micro instance in a particular zone and nothing else, for the duration of my timeslice the VM will have to monopolize the core. Optimal use of vCPUs would demand that two VM threads get scheduled to the core to take advantage of HT, which Google says it won’t do. Timeslicing doesn’t solve this problem. At least that’s my reading of what they said.

Re-read what I wrote above. It covered both simultaneous and sequential sharing. Here is the part you are concerned about: instances do not simultaneously share cores with other customer instances via SMT.

Re-read what I wrote. Imagine a machine with 8 cores and 16 hyperthreads. Now imagine you need to optimally use the execution ports in each core. To do that you would need to have 16 VM threads all feeding the ports simultaneously, 2 per core. If all your workloads on that machine are from different customers, you can’t do more than 8. If you timeslice more than 8, then the question is, what is it that you’re selling as a vCPU? If it’s a timesliced core, then it’s not what they say they’re selling (a hyperthread).

You:

> If it’s a timesliced core, then it’s not what they say they’re selling (a hyperthread).

vs.

_msw_:

> A core can be sequentially time sliced between customer instances when you use a fractional (m3.medium) or burst (T2 instances) CPU instance type.

AWS instance types page ( https://aws.amazon.com/ec2/instance-types/ ):

> Each vCPU is a hyperthread of an Intel Xeon core except for T2 and m3.medium.

Not in Google’s case. There vCPU == hyperthread. To quote https://cloud.google.com/compute/docs/machine-types: "For the n1 series of machine types, a vCPU is implemented as a single hardware hyper-thread". One more area where Google is more explicit. Only their partial vCPU instances are timesliced: "Shared-core machine types provide one vCPU that is allowed to run for a portion of the time on a single hardware hyper-thread on the host CPU running your instance".

Except this thread has been about AWS, not Google.

Who cares how Google defines things?

It was about both.

> Optimal use of vCPUs would demand that two VM threads get scheduled to the core to take advantage of HT

It would.

So those cores won't be used optimally. No big deal.

Yeah, and the throughput of HT threads on an already busy core was not that high, last I checked.

timeslicing works fine, you just have to flush the cache when switching

I’m not disputing that. I’m just saying that for the specific case of jobs with 1 vCPU which are all from different users you can only schedule half the billable capacity.

Or map pairs of hyperthreads to each requested vCPU, or disable hyperthreading. Which kills co-tenancy overcommit and makes the infra more expensive for a cloud provider.