> no IO is performed

A DB that performs no IO? Can you elaborate?

Referring to this sentence, I think:

>To test CPU performance, I used a read-only in-memory sysbench OLTP benchmark, as it burns CPU cycles and no IO is performed by Percona Server.

Usually that means a read-heavy workload where things fit in RAM.

That's a literal quote from the article. The benchmark was done entirely done in-memory.

There is no such thing as no I/O.

If you're latency bound by the round trip to main memory then SMT will still have a noticeable benefit. The most important thing it can't help with is if you are compute bound.

Nobody calls "trips to memory" I/O though. Yes SMT can have a benefit but the OP was asking about the case with more threads than logical cores, so SMT is already maxed out (assuming all threads are CPU bound).

> SMT will still have a noticeable benefit

YMMV. SMT usually halves the cache size usable by each thread. If your memory access is heavily local, enabling SMT can hurt your performance.