So what comes after parallel processing?

[alephnull]

jlauro said:

MisterBlonde said:
@jlauro

A function call is single assembly instruction.

Scheduling a thread for execution requires determining which thread from the pool to schedule time (Threads have different priorities, different states). Additionally the scheduler would have to preempt currently running threads, save their context (state of the CPU registers at the time the thread was interrupted), and then load the context into registers from the thread that is getting scheduled for execution.

Certainly all that stuff could possibly be optimized more in the future, but nevertheless it will always be a lot more expensive than a single function call. The more threads and cores the scheduler has to deal with the more complex it becomes and the more often it happens.

That is only an issue if the scheduler is done in software. A hardware scheduler could easily look at all the threads once per clock cycle, even if there were thousands of cores. It's faster to do that then adding two 64 bit numbers together in hardware, which typically only takes one cycle. That is what is so cool with hardware. The os could impose resource limits in register as to how many threads are allowed to be automatically created before a request has to be approved or rebalanced by the os, or to only go back to the os if no open threads are available. Remember, in this hypothetical environment there are lots of cores, and you shoud never run out except on the busiest servers at peek time.

 

I don't see how your hardware schedualer would help reduce the overhead for context switches. And I think you are overestimating the power of hardware schedualers and underestimating the problem.

Calculating the optimal schedual on an SMP system is equivalent to bin packing, which is NP hard

Once apon a time my area of research in CS was multiprocessor hybrid (EDF, RM, and fixed priority schedualing) for realtime schedualers. While the schedualing algorithms are somewhat different for normal systems, I do know something about it.