Limiting CPU Threads for Better Game Performance

The Secret to Better Game Performance: Limiting CPU Threads

Summary

In the quest for smoother gaming experiences, developers often overlook a crucial factor: CPU thread management. Contrary to popular belief, more threads do not always mean better performance. In fact, limiting CPU threads can significantly improve game performance on high-end systems. This article delves into the reasons behind this phenomenon and provides practical solutions for developers to optimize their games.

The Problem with Too Many Threads

High-end CPUs with more than 8 cores can sometimes render games faster with half their thread counts. This is because not all threads are equal. Physical threads (cores) differ from logical threads born out of hyperthreading, and the P-cores on Intel’s hybrid processors are more potent than the accompanying low-power E-cores. Consequently, game developers are better off limiting their code to fewer CPU threads to maximize performance and minimize complexity.

Why Fewer Threads Can Be Better

1. Hardware Performance: Higher-core-count CPUs sometimes have lower CPU speeds. Reducing the number of threads may enable the active cores to boost their frequency.
2. Hardware Resource Contention: Reducing the thread count can decrease the pressure on the memory subsystem, reducing latency and enabling the CPU caches to be more efficient. This is especially true for chiplet-based architectures that do not have a unified L3 cache.
3. Software Resource Contention: Locks and atomics can have much higher latency when accessed by many threads concurrently, adding to the memory pressure. False sharing can exacerbate this.
4. OS Scheduling Issues: An over-subscription of threads to active cores leads to a high number of context switches which can be expensive and can put extra pressure on the CPU memory subsystem.
5. Power Management: Reducing the number of threads can enable more cores to be parked, saving power and potentially allowing the remaining cores to run at a higher frequency.

Practical Solutions

1. Dynamic Load Balancing: Dynamically adjust thread counts based on workload.
2. Lockless Threading Models: Use lockless threading models that scale with core count.
3. QoS and Thread Priority APIs: Use QoS and thread priority APIs to help steer threads to specific cores.
4. Thread Count Determination: Tailor thread counts to fit the workload. Test different thread counts and find a sweet spot for your game.

Testing and Optimization

1. Test on Different Systems: Test your game on different systems at different settings and with different thread counts.
2. Hyperthreading: Test hyperthreading to see whether you should align to physical or logical cores when enumerating your threads on different systems.
3. Thread Count Override: Provide an override for thread count in an .ini file to ensure that gamers can find the right value to maximize performance on their PC.

Table: Performance Gains from Reducing Thread Counts

Additional Tips

1. Avoid Over-Subscription: Avoid over-subscribing threads to active cores to prevent high context switch rates.
2. Use Physical Cores: Target physical core counts instead of logical core counts to reduce latency.
3. Test Hyperthreading: Test hyperthreading to see whether it helps or hinders performance on your game.

By following these tips and understanding the importance of limiting CPU threads, developers can create games that run smoother and faster on a variety of systems.

Conclusion

Limiting CPU threads can significantly improve game performance on high-end systems. By understanding the reasons behind this phenomenon and implementing practical solutions, developers can optimize their games for smoother gaming experiences. Remember, fewer threads can sometimes be better, and tailoring thread counts to fit the workload is key to achieving maximum performance.