Multiple Software Layers Research Articles

I/O Access Patterns in HPC Applications: A 360-Degree Survey

The high-performance computing I/O stack has been complex due to multiple software layers, the inter-dependencies among these layers, and the different performance tuning options for each layer. In this complex stack, the definition of an “I/O access pattern” has been reappropriated to describe what an application is doing to write or read data from the perspective of different layers of the stack, often comprising a different set of features. It has become common to have to redefine what is meant when discussing a pattern in every new study, as no assumption can be made. This survey aims to propose a baseline taxonomy, harnessing the I/O community’s knowledge over the past 20 years. This definition can serve as a common ground for high-performance computing I/O researchers and developers to apply known I/O tuning strategies and design new strategies for improving I/O performance. We seek to summarize and bring a consensus to the multiple ways to describe a pattern based on common features already used by the community over the years.

Integrating LSM Trees With Multichip Flash Translation Layer for Write-Efficient KVSSDs

Log-structured-merge (LSM) trees are a highly write-optimized data structure for lightweight, high-performance key-value (KV) stores. Furthermore, solid-state drives (SSDs) are a crucial component for I/O acceleration. Conventional LSM-over-SSD designs involve multiple software layers, including the LSM tree, host file system, and flash translation layer (FTL), which introduce cascading write amplifications. To manage the write amplifications from different layers, we propose KVSSDs, which are a close integration of LSM trees and the FTL. KVSSDs exploit the FTL mapping mechanism to implement copy-free compaction of LSM trees, and they enables direct data allocation in flash memory for efficient garbage collection. Our design also uses a fine-grained, dynamic striping policy to fully exploit the rich internal parallelism of multichip SSDs. The experimental results indicated that our LSM-SSD integrated design reduced the write amplification by 86% and improved the throughput by 383% compared with a conventional LSM-over-SSD design.

S-WAL: Fast and Efficient Write-Ahead Logging for Mobile Devices

A crash-consistency mechanism of database application (hereinafter DBMS for short) imposes an enormous burden on the journaling process of the file system (e.g., JBD2) in that it employs regular files on the file system to persistently preserve the application’s journal data with synchronous system calls. Unfortunately, much of the previous research is impractical in real-world scenarios because they require changing a lot of source lines of code in multiple software layers of the software stack or using special hardware (e.g., the transactional flash storage or NVM technologies). In this paper, we propose a new journal mode of DBMS, called S-WAL, which compresses the raw data journaled by the database to alleviate both the redundant journaling operations and harmful write amplification. We believe that S-WAL is a practical way to support application-level crash consistency on the existing mobile devices because only a few lines of DBMS code need to be changed, without the need to employ special hardware. We demonstrate the effectiveness of S-WAL by running four popular mobile applications on the latest smartphone. Our evaluation results show that S-WAL considerably outperforms existing journal modes of DBMS in all cases. In the best case, S-WAL reduces the elapsed time by up to $7.5\times$ more than the PERSIST mode and by up to 51% more than the traditional WAL mode.

I/O access frequency-aware cache method on KVM/QEMU

Together with the rapid development of IT technology, cloud computing has been considered as the next generation's computing infrastructure. One of the essential part of cloud computing is the virtual machine technology that enables to reduce the data center cost with better resource utilization. Especially, virtual desktop infrastructure (VDI) is receiving explosive attentions from IT markets because of its advantages of easier software management, greater data protection, and lower cost. However, sharing physical resources in VDI to consolidate multiple guest virtual machines (VMs) on a host has a tradeoff that can lead to significant I/O degradation. Optimizing I/O virtualization overhead is a challenging task because it needs to scrutinize multiple software layers between guest VMs and host where those VMs are executing. In this paper, we present a hypervisor-level cache, called hyperCache, which is possible to provide a shortcut in KVM/QEMU. It intercepts I/O requests in the hypervisor and analyses their I/O access patterns to select data retaining high access frequency. Also, it has a capability of maintaining the appropriate cache memory size by utilizing the cache block map. Our experimental results demonstrate that our method improves I/O bandwidth by up to 4.7x over the existing QEMU.

MultiCache: Multilayered Cache Implementation for I/O Virtualization

As the virtual machine technology is becoming the essential component in the cloud environment, VDI is receiving explosive attentions from IT market due to its advantages of easier software management, greater data protection, and lower expenses. However, I/O overhead is the critical obstacle to achieve high system performance in VDI. Reducing I/O overhead in the virtualization environment is not an easy task, because it requires scrutinizing multiple software layers of guest-to-hypervisor and also hypervisor-to-host. In this paper, we propose multilayered cache implementation, called MultiCache, which combines the guest-level I/O optimization with the hypervisor-level I/O optimization. The main objective of the guest-level optimization is to mitigate the I/O latency between the back end, shared storage, and the guest VM by utilizing history logs of I/O activities in VM. On the other hand, the hypervisor-level I/O optimization was implemented to minimize the latency caused by the “passing I/O path to the host” and the “contenting physical I/O device among VMs” on the same host server. We executed the performance measurement of MultiCache using the postmark benchmark to verify its effectiveness.

Multi-layer software reliability for unreliable hardware

Abstract This paper presents a multi-layer software reliability approach that leverages multiple software layers (e. g., programming language, compiler, and operating system) to improve the overall system reliability considering unreliable or partly-reliable hardware. We present a comprehensive design flow that integrates multiple software layers while accounting for the knowledge from lower hardware layers. We show how multiple software layers synergistically operate to achieve a high degree of reliability.

Booting, browsing and streaming time profiling, and bottleneck analysis on android-based systems

Android-based systems perform slowly in three scenarios: booting, browsing, and streaming. Time profiling on Android devices involves three unique constraints: (1) the execution flow of a scenario invokes multiple software layers, (2) these software layers are implemented in different programming languages, and (3) log space is limited. To compensate for the first and second constraints, we assumed a staged approach using different profiling tools applied to different layers and programming languages. As for the last constraint and to avoid generating enormous quantities of irrelevant log data, we began profiling scenarios from an individual module, and then iteratively profiled an increased number of modules and layers, and finally consolidated the logs from different layers to identify bottlenecks. Because of this iteration, we called this approach a staged iterative instrumentation approach. To analyze the time required to boot the devices, we conducted experiments using off-the-shelf Android products. We determined that 72% of the booting time was spent initializing the user-space environment, with 44.4% and 39.2% required to start Android services and managers, and preload Java classes and resources, respectively. Results from analyzing browsing performance indicate that networking is the most significant factor, accounting for at least 90% of the delay in browsing. With regard to online streaming, networking and decoding technologies are two most important factors occupying 77% of the time required to prepare a 22MB video file over a Wi-Fi connection. Furthermore, the overhead of this approach is low. For example, the overhead of CPU loading is about 5% in the browsing scenario. We believe that this proposed approach to time profiling represents a major step in the optimization and future development of Android-based devices.

Application of contract-based security assertion monitoring framework for telecommunications software engineering

Telecommunication software systems, containing security vulnerabilities, continue to be created and released to consumers. We need to adopt improved software engineering practices to reduce the security vulnerabilities in modern systems. Contracts can provide a useful mechanism for the identification, tracking, and validation of security vulnerabilities. In this work, we propose a new contract-based security assertion monitoring framework (CB_SAMF) that is intended to reduce the number of security vulnerabilities that are exploitable across multiple software layers, and to be used in an enhanced systems development life cycle (SDLC). We show how contract-based security assertion monitoring can be achieved in a live environment on Linux. Through security activities integrated into the SDLC we can identify potential security vulnerabilities in telecommunication systems, which in turn are used for the creation of contracts defining security assertions. Our contract model is then applied, as runtime probes, against two common security related vulnerabilities in the form of a buffer overflow and a denial of service.