This thesis aims to address the growing disconnect between the goals general-purpose operating systems were designed to achieve and the requirements of some of today’s new workloads and use cases. General-purpose operating systems multiplex system resources between multiple non-trusting workloads and users. They have generalized code paths, designed to support diverse applications, potentially running concurrently. This generality comes at a performance cost. In contrast, many modern data center workloads are often deployed separately in single-user, and often single workload, virtual machines and require specialized behavior from the operating system for high-speed I/O.
Unikernels, library operating systems, and systems that exploit kernel bypass mechanisms have been developed to provide high-speed I/O by being specialized to meet the needs of performance-critical workloads. These systems have demonstrated immense performance advantages over general-purpose operating systems but have yet to see widespread adoption. This is because, compared to general-purpose operating systems, these systems lack a battle-tested code base, a large developer community, wide application, and hardware support, and a vast ecosystem of tools, utilities, etc.
This thesis explores a novel view of the design space; a generality-specialization spectrum. General-purpose operating systems like Linux lie at one end of this spectrum; they are willing to sacrifice performance to support a wide range of applications and a broad set of use cases. As we move towards the specialization end, different specializable systems like unikernels, library operating systems, and those that exploit kernel bypass mechanisms appear at different points based on how much specialization a system enables and how much application and hardware compatibility it gives up compared to general-purpose operating systems.
Is it possible, at compile/configure time, to enable a system to move to different points on the generality-specialization spectrum depending on the needs of the workload? Any application would just work at the generality end, where application and hardware compatibility and the ecosystem of the general-purpose operating system are preserved. Developers can then focus on optimizing performance-critical code paths only, based on application requirements, to improve performance. With each new optimization added, the set of target applications would shrink. In other words, the system would be specialized for a class of applications, offering high performance for a potentially narrow set of use cases.
If such a system could be designed, it would have the application and hardware compatibility and ecosystem of general-purpose operating systems as a starting point. Based on the target application, select code paths of this system can then be incrementally optimized to improve performance, moving the system to the specializable end of the spectrum. This would be different from previous specializable systems, which are designed to demonstrate huge performance advantages over general-purpose operating systems, but then try to retrofit application and hardware compatibility. To explore the above question, this thesis proposes Unikernel Linux (UKL), which integrates optimizations explored by specializable systems to Linux. It starts at the general-purpose end of the spectrum and, by linking an application with the kernel, kernel mode execution, and replacing system calls with function calls, offers a minimal performance advantage over Linux. This base model of UKL supports most Linux applications (after recompiling and relinking) and hardware. Further, this thesis explores common optimizations explored by specializable systems, e.g., faster transitions between application and kernel code, avoiding stack switches, run-to-completion modes, and bypassing the kernel TCP state machine to access low-level functions directly. These optimizations allow higher performance advantages over unmodified Linux but apply to a narrower set of workloads.
Contributions of this thesis include proposing a novel approach to specialization, i.e., adding optimizations to a general-purpose operating system to move it along the generality-specialization spectrum, an existence proof that optimizations explored by specializable systems can be integrated into a general-purpose operating system without major changes to the invariants, assumptions, and code of that general purpose operating system, a demonstration that the resulting system can be moved on the generality-specialization spectrum, and showing that performance gains are possible.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49225 |
| Date | 10 September 2024 |
| Creators | Raza, Ali |
| Contributors | Krieger, Orran |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0/ |
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