Does multithreading always yield better performance than single threading?

Question

I know the answer is No, here is an example Why single thread is faster than multithreading in Java? .

So when processing a task in a thread is triv

Answer 1

Not all algorithms can be processed in parallel (algorithms that are strictly sequential; where P=0 in Amdahl's law) or at least not efficiently (see P-complete). Other algorithms are more suitable for parallel execution (extreme cases are called "embarrassingly parallel").

A naive implementation of a parallel algorithm can be less efficient in terms of complexity or space compared to a similar sequential algorithm. If there is no obvious way to parallelize an algorithm so that it will get a speedup, you may need to choose another similar parallel algorithm that solves the same problem but can be more or less efficient. If you ignore thread/process creation and direct inter-process communication overhead, there can still be other limiting factors when using shared resources like IO bottlenecks or increased paging caused by higher memory consumption.

When should we decide to give up multithreading and only use a single thread to accomplish our goal?

When deciding between single and multithreading, the time needed to change the implementation and the added complexity for developers should be taken into account. If there is only small gain by using multiple threads you could argue that the increased maintenance cost that are usually caused by multi-threaded applications are not worth the speedup.