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Comment by mdriley | Hacker News Reader

Eric Brandwine (VP/DE @ AWS) said publicly in 2019 that EC2 had never scheduled different tenants on the same physical core at the same time, even before we learned about things like MDS.

https://youtu.be/kQ4H6XO-iao?t=2485

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How does that work for burstable VMs? Surely they must be oversubscribed on a per-core basis? Are they sharing cores, but doing scheduling at a very fine granularity (eg. millisecond)?

I guess they can only schedule hyperthreads if the same tenant requests at least two virtual cores?

I don't think it really matters, the goal post will move to LLC attacks. As long as you have caching involved, I wouldn't bet anything can run "safely".

I wonder if per-tenant cache structures might become more popular in the future. It isn't unimaginable that different tenants will be running different things anyway, so split caches might still keep a reasonable amount of effectiveness.

That's a really good talk. Wish I'd watched it around the time the speculative execution vulnerabilities were all the talk.

I'm not qualified in computer science or programming but I could easily follow along with his explanation about challenging CPU architectural concepts. Gives me a great deal of confidence that AWS not only know what they're doing, but can communicate it well to management.

ReInvent 2019 was a magical place. Watching many of the videos from that conference helped my career a lot. The quality for the most part of the content is outstanding.

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