In multiprocessor operating systems, which of the following lists common thread scheduling strategies used to distribute work across multiple CPUs?

Introduction / Context:
On multiprocessor or multicore systems, the operating system must decide how to place threads on available processors. Efficient scheduling strategies are important for achieving good performance and cache utilisation. This question checks whether you can recognise widely discussed multiprocessor thread scheduling approaches used in operating system design.

Given Data / Assumptions:

• The system has more than one processor or core available.
• Threads can be executed on different processors.
• Scheduling can consider load distribution and relationships between threads.
• No numeric calculations are involved.

Concept / Approach:
Common multiprocessor thread scheduling strategies include load sharing, where the operating system attempts to balance runnable threads across processors, and processor affinity scheduling, where a thread tends to run on the same processor to take advantage of warm caches. Gang scheduling is another strategy where related threads of a parallel application are scheduled to run simultaneously on different processors so that they can synchronise efficiently. These strategies contrast with simple single processor algorithms or naive random assignment that ignore load and affinity considerations.

Step-by-Step Solution:
Step 1: Recall that multiprocessor scheduling must address both load balance and locality of reference. Step 2: Identify load sharing as the policy that spreads threads so no processor is heavily overloaded while others are idle. Step 3: Recognise processor affinity as keeping a thread on the same CPU when possible to benefit from cache contents. Step 4: Recognise gang scheduling as running groups of related threads together on different processors to support tight synchronisation. Step 5: Select the option that lists these three recognisable strategies and discard options that ignore multiprocessor concerns.

Verification / Alternative check:
Operating systems textbooks and research papers on multiprocessor scheduling repeatedly mention load sharing, affinity and gang scheduling as fundamental approaches. Real systems often implement some combination of these ideas. They rarely, if ever, rely on purely random selection or limit themselves to single processor algorithms when multiple processors are present, which supports the choice of the correct option.

Why Other Options Are Wrong:
Option B describes first come first served on a single processor, which does not exploit multiple processors or address load balancing. Option C advocates random assignment, which usually leads to poor performance and unpredictable cache behaviour. Option D suggests scheduling based only on user input devices, which is unrelated to general multiprocessor thread scheduling strategies used by operating systems.

Common Pitfalls:
Learners sometimes assume that single processor scheduling policies automatically scale to multiprocessor systems without modification, overlooking issues like cache affinity and synchronisation needs. Another mistake is to underestimate the importance of scheduling related threads together; if they are spread across processors at different times, communication and barrier synchronisation can become very slow.

Final Answer:
Typical multiprocessor thread scheduling strategies include load sharing, processor affinity scheduling and gang scheduling of related threads.