Spinning around: Please don't – Common problems with spin locks
10 days ago
- #performance
- #spin-locks
- #multithreading
- Spin-loops are problematic and often lead to the same recurring issues.
- Implementing a spin-lock incorrectly can cause race conditions and thread safety issues.
- Atomic operations can mitigate race conditions but require careful usage.
- Empty spin loops can burn CPU cycles and waste energy, impacting performance and power consumption.
- The PAUSE instruction on x86 CPUs helps mitigate the negative effects of spin loops.
- Exponential backoff strategies can reduce contention and improve performance in spin-locks.
- The duration of PAUSE instructions varies significantly across CPU architectures, requiring careful tuning.
- Memory order parameters in atomic operations can impact performance; using acquire/release semantics can be more efficient.
- Avoiding unnecessary memory barriers and optimizing cache usage can improve spin-lock performance.
- Priority inversion is a serious issue with spin-locks, especially in real-time systems.
- Using OS primitives like futex (Linux) or WaitOnAddress (Windows) can improve fairness and reduce contention.
- False sharing can degrade performance; aligning variables or using padding can help mitigate this.
- Specialized instructions like MWAIT and TPAUSE can offer performance benefits but are often privileged.
- Spin-locks should only be used in low-contention scenarios with very short critical sections.
- Many projects and libraries have implemented spin-locks incorrectly, leading to performance issues or livelocks.