Application-Informed Kernel Synchronization Primitives

Kernel synchronization primitives are the backbone of any OS design. Kernel locks, for instance, are crucial for both application performance and correctness. However, unlike application locks, kernel locks are far from the reach of application developers, who have minimal interpolation of the kernel's behavior and cannot control or influence the policies that govern kernel synchronization behavior. This disconnect between the kernel and applications can lead to pathological scenarios in which optimizing the kernel synchronization primitives under one context, such as high contention, leads to adversarial effects under a context with no lock contention. In addition, rapid-evolving heterogeneous hardware makes kernel lock development too slow for modern applications with stringent performance requirements and frequent deployment timelines.

This paper addresses the above issues with applicationinformed kernel synchronization primitives. We allow application developers to deploy workload-specific and hardwareaware kernel lock policies to boost application performance, resolve pathological usage of kernel locks, and even enable dynamic profiling of locks of interest. To showcase this idea, we design SynCord, a framework to modify kernel locks without recompiling or rebooting the kernel. SynCord abstracts key behaviors of kernel locks and exposes them as APIs for designing user-defined kernel locks. SynCord provides the mechanisms to customize kernel locks safely and correctly from the user space. We design five lock policies specialized for new heterogeneous hardware and specific software requirements. Our evaluation shows that SynCord incurs minimal runtime overhead and generates kernel locks with performance comparable to that of the state-of-the-art locks.