process thread scheduling

Question

I have the following query regarding the scheduling of process threads. a) If my process A has 3 threads then can these threads be scheduled concurrently on the different CPUs in SMP m/c or they will be given time slice on the same cpu.

b) Suppose I have two processes A with 3 threads and Process B with 2 threads (all threads are of same priority) then cpu time allocated to each thread (time slice) is dependent on the number of threads in the process or not? Correct me if I am wrong is it so that cpu time is allocated to process which is then shared among its threads i.e. time slice given to process A threads is less than that of Process B threads.

Answer 1

This depends on your OS and thread implementation. POSIX threads defines an interface for defining how threads are scheduled: whether each thread is scheduled equally or each process is scheduled equally. Not all scheduling types are supported on all platforms.

On Linux, using nptl, the default behavior is to schedule all threads equally, so a process with 10 threads might get 10 times as much time as a process with 1 thread, if all eleven threads are CPU bound.