Question

In order to fully utilize multiprocessor machines, it is important to guarantee that we
use kernel-level thread libraries over multithreaded kernel.

a)Compare the performance if we use a user-level thread library on top of (i)
non-multithreaded kernel or (ii) multithreaded kernel. Are their performance similar or (i)
is better than (ii) or (ii) is better than (i)? Justify your answer.
b) Discuss whether blocking problem occurs for both cases in (a). The blocking
problem here means that if one user-level thread is blocked, the whole system is blocked.

Answer 1

a) Performance of Multithreaded Kernel is better than Non-Multithreaded kernel because of the following reasons:

1) Responsiveness- Let's suppose a Process which is using Multithreaded environment , if one of the threads is blocked due to some reason than it does not mean that the whole program stopped working. You can use various other threads in that Program to run it. For eg: In a Application, If one thread is downloading any files than you can also view the Webpage or interact with the application at the same time. It is due to the Multithreading environment.

If we talk about non-multithreaded environment, than in that case whole program gets blocked if the thread is blocked

2)Resource Sharing- By deafult,threads share the memory and the resources of the process to which they belong.The benifits of sharing code and data is that it allows an application to have different threads of activity within the same addess space.But we cannot do this thing in Non-Multithreaded Environment

3)Utilisation of Multiprocessor Architectures- The Benifit of Multithreading can be in a Multiprocessor architecture,where threads may be running in parallel on different processors,so making it more efficient. A single threaded process can only be run on one CPU, no matter how many CPU (processors) are available. Multithreading on a multi-CPU machine increases concuurency

So, these above 3 points Justify my answer that Multithreading Kernel is Better and Efficient than Non-Multithreading Kernel

Let's Talk about Blocking of the thread in User Level and Kernel Level:

. If we talk about blocking than if one of the threads is blocked in user level than whole process will be blocked but in Kernel-level if one of the threads of the kernel level is blocked than this results no affects on another threads,therefore the process will not stop.

Why this Happens?

With kernel threads, the kernel is aware of all of the threads inside the process, because the kernel created them (on behalf of the application) and manages them directly, so the kernel can schedule any of them directly. Because of that, when thread A blocks inside a system call, the kernel/scheduler can go ahead and run thread B for a while instead, because the kernel knows that thread B exists. (Contrast this with the user-threads case, where the kernel can't schedule thread B to run, because the kernel doesn't know that thread B exists; only the user-application itself knows about the existence of the user-level threads)