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Advanced Topic 51 of 51 Operating Systems

Scheduling in Multiprocessors

Balancing load and affinity across CPU cores.

How it works

Multiprocessor scheduling assigns threads to several CPUs. Designs use one global run queue, simple but contended, or per-CPU run queues with load balancing through migration. Processor affinity keeps a thread on the same core to preserve warm caches, and NUMA-aware scheduling places threads near their memory. Gang scheduling runs related threads together, and symmetric multiprocessing treats all cores equally while asymmetric designs like big.LITTLE mix core types.

Step-by-step walkthrough

  1. Each core has its own run queue.
  2. Tasks stay on one core to reuse its cache, called affinity.
  3. One core is overloaded and another idle.
  4. The scheduler migrates tasks to balance load.
  5. Balance versus cache warmth is the key trade-off.

Where it is used

Servers, desktops, phones and cloud hypervisors rely on multiprocessor schedulers to keep cores busy and efficient while saving power. Pinning threads is used in latency-sensitive and high-performance applications.

Common pitfall

Migrating threads too often loses cache contents, but unbalanced queues leave cores idle. Lock contention on shared structures limits scalability. Ignoring NUMA causes slow remote memory accesses, and hyperthreading siblings share resources. Measure with perf and use affinity, cpusets or cgroup limits deliberately rather than by habit.

Where it fits in the course

Scheduling in Multiprocessors is topic 51 of 51 in Operating Systems, rated Advanced. It follows Linux Kernel Internals. It is the last topic in this area.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Operating Systems quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Scheduling in Multiprocessors?
Balancing load and affinity across CPU cores. It belongs to Operating Systems and is an advanced-level topic.
Where do people use Scheduling in Multiprocessors?
Servers, desktops, phones and cloud hypervisors rely on multiprocessor schedulers to keep cores busy and efficient while saving power.
What is the most common mistake with Scheduling in Multiprocessors?
Migrating threads too often loses cache contents, but unbalanced queues leave cores idle.
What should I learn before this topic?
Start with Linux Kernel Internals, the topic just before it in Operating Systems.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Operating Systems quiz.
Is Scheduling in Multiprocessors hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn Scheduling in Multiprocessors?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Scheduling in Multiprocessors?
Linux Kernel Internals, Microkernels vs Monolithic Kernels, Namespaces and Cgroups are closely connected. The full list is in the related topics section of this page.
What should I study after Scheduling in Multiprocessors?
You have reached the last topic in Operating Systems. Pick another area on the Learn page, or revisit this topic with the quiz.

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