Modern Computers are multi modal for a lot of resources access : IO/CPU/locks/Context Switch/IRQ/memory/L1/L2/L3...
What does a modal change means? Frequency changes. Basically the system have 3 main mode Fast/intermittent/slow access.
EX: when cache is full pointer_p = x is ~= 400cycles else it can go up to 15000cycles.
The problem is the modal change between resources accesses comes with sharp unpredictable transitions and that they are tightly coupled together.
Memory over use overflow L1/L2/L3 in swap that triggers another mode in the pattern of IO. And slow memory access impact the access to the data structure needed to treat the HW data stream ...
At the congestion (when computers are heavily sollicited) tightly coupled interaction coming from code written in non controlled way tends to do a snowball effect, creating an avalanche of bad behaviours that makes any important resources access pattern switch from slow/fast access in a way that parasite other resources. Chaotically.
Why is the code uncontrolled? Almost all optimization are made by complex code that Intel put into the CPU on the silicium. So your code is uncontrolled whether you like it or not. And that what this guy complain about. Not complexity of Intel CPU but complication.
Our unit test makes at best uni dimensional stress tests. While the true world has between n and n * (n - 1) potential coupling behaviour at most where n is the number of potential coupling. (We have quite a lot of resources HPET1/2/3 IRQ, context switches).
The number of mathematical combination of behaviour that netflix/google/amazon/intel pretend to control are just NOT possibly coverable.
What does it mean? It mean no one should engage its trust in using modern computers to do any heavy load critical tasks.
At the opposite of old computers we cannot use them at full capacity and we don't know what is the safe load so we had even more coupling and complexity and chaos to the architecture.
The problem is means increasingly fast diminishing operation/watt efficiency.
The throughput of energy that humanity can collect per unit of time is bounded.
Old devs that did Hardware know modern IT are heading the wrong direction. But, business men don't care, journalists interview the successful business men, not the coders that are doing the actual job and know how the machinery behaves.