Re:Understanding L1 Terminal Fault aka Foreshadow: What You ...
by h4b4n3r0 on Tuesday August 14, 2018 @10:53PM
(#17763445)
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).
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Re:Understanding L1 Terminal Fault aka Foreshadow: What You ...
by cthalupa on Wednesday August 15, 2018 @02:28AM
(#17764108)
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.
Re:Understanding L1 Terminal Fault aka Foreshadow: What You ...
by h4b4n3r0 on Wednesday August 15, 2018 @04:39AM
(#17764538)
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".