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Comment by electic | Hacker News Reader

This is going to have dramatic effect on the cloud computing market. It might make sense to make sure any VMs you run are on AMD processors or it can really hurt your performance and basically cost you more to do the same workload.

It also seems, from early benchmarks, this can slaughter performance with databases.

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Here's a Postgres benchmark on Skylake (supports PCID) showing a ~6% reduction in TPS.

http://lkml.iu.edu/hypermail/linux/kernel/1801.0/01274.html

I wonder if cloud providers will ask Intel for partial refunds when their CPUs get 5% to 30% slower than promised?

Why? They pass it on to customers. More interesting if Google or Facebook will react. They could need up to a data centre each to compensate for that (I assume both have very syscall heavy applications). Maybe not suing Intel but pouring more money into the development of competing chips

Why are people insisting this affects cloud computing market? I am not sure if this bug is absolutely limited to cloud instances.

Because for example most consumers don't care.

Because this bug allegedly affects hypervisors/VMs.

But shouldn’t the fix affect the kernel performance regardless of whether the OS system is a guest or not?

The bug affects transistions into kernel mode. Virtual machines have one extra transistion. A read() call in the guest calls the guest OS which calls the host OS.

You are referring to the slow down and hence the extra slow down for calling an extra syscall?

If so, then isn't it technically correct that the bug will affect regardless of virtualization or not, but heavier penalty for VMs?

Don't worry. I don't think that there will be two separate kernels for Intel and AMD. I think performance drop will be on both CPUs no matter has it the bug or not.

You can turn it off and on via a commandline flag.

No. The check is being made what CPU is underlying before applying the fix.

Not yet. That patch hasn't been merged as of now.

Probably because the method of checking is flawed and should be done in make/model (i'm no kernel expert but this is the general oppinion i've seen so far).

I've seen nothing except the 'caution side lets do it with all' approach and no indication of other problems on the other hand.

You could just compile the kernel without it on?

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