A Dynamic Software Update (DSU) system enables an operator to modify a running program without interrupting its execution. However, creating a DSU system to allow programs written in the C programming language to be modified while they are executing is challenging. This paper presents the Portable Software Update (PSU) system, a new framework that allows the creation of C-language DSU programs. PSU offers a simple programming interface to build DSU versions of existing C programs. Once a program is built using PSU, updates can be applied by background threads that have negligible impact on the execution of the program. PSU supports multi-threaded and recursive programs without the use of safe points or thread blocking. PSU uses function indirection to redirect DSU functions calls to the newest version of the function code. Once a DSU function is invoked in a PSU program, it executes to completion using the version of the function that was active when it was invoked. However, if a new version is installed, any future calls to the same function always execute the newest version. This simple mechanism allows for quick loading of updates in PSU. PSU unloads obsolete version of DSU functions after they are no longer executing. This mechanism makes PSU the first DSU system for C-language programs that is able to unload older versions of code. This efficient use of resources enables many patches to be applied to a long-running application. A suite of specialized custom synthetic programs, and a DSU-enabled version of the MySQL database storage engine, are used to evaluate the overhead of the DSU-enabling features. The MySQL storage engine maintains over 95% of the performance of the non-DSU version and allows the entire storage engine to be updated while the database continues executing. PSU includes a simple and straightforward process for the modification of the storage engine that enables DSU.

We present Replayable Execution, a system for improving the efficiency of Function-as-a-Service (FaaS) frameworks. It takes advantage of standard kernel features to reduce memory usage and accelerate cold startup speed without changes to the OS kernel, language runtimes, and the surrounding FaaS deployment environment. Replayable Execution exploits the intensive-deflated execution characteristics of the majority of target applications. It uses checkpointing to save an image of an application, allowing this image to be shared across containers and resulting in speedy restoration at service startup. We apply Replayable Execution to a representative FaaS Java framework to create a ReplayableJVM execution, which together with benefits from deterministic execution of a warmed up runtime, offers 2X memory footprint reduction, and over 10X startup time improvement.

Feedback-directed optimization is an effective technique to improve program performance, but it may result in program performance and compiler behavior that is sensitive to both the selection of inputs used for training and the actual input in each run of the program. Cross-validation over a workload of inputs can address the input-sensitivity problem, but introduces the need to select a representative workload of minimal size from the population of available inputs. We present a compiler-centric clustering methodology to group similar inputs so that redundant inputs can be eliminated from the training workload. Input similarity is determined based on the compile-time code transformations made by the compiler after training separately on each input. Differences between inputs are weighted by a performance metric based on cross-validation in order to account for code transformation differences that have little impact on performance. We introduce theCrossErrormetric that allows the exploration of correlations between transformations based on the results of clustering. The methodology is applied to several SPEC benchmark programs, and illustrated using selected case studies.