Browsing by Author "JU, Lei"

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    Managing Tenants in a Multi-tenant SaaS
    (2010-10-28T03:38:36Z) JU, Lei; BANERJEE, Ansuman; ROYCHOUDHURY, Abhik; SENGUPTA, Bikram
    A multi-tenant software as a service (SaaS) system has to meet the needs of several tenant organizations, which connect to the system to utilize its services. To leverage economies of scale through reuse, a SaaS vendor would, in general, like to drive commonality amongst the requirements across tenants. However, many tenants will also come with some custom requirements that may be a prerequisite for them to adopt the SaaS system. These requirements then need to be addressed by evolving the SaaS system in a controlled manner, while still supporting the requirements of existing tenants. In this paper, we study the challenges associated with engineering multi-tenant SaaS systems and develop a framework to help evolve and validate such systems in a systematic manner. We adopt an intuitive formal model of services. We show that the proposed formalism is easily amenable to tenant requirement analysis and provides a systematic way to support multiple tenant onboarding and diverse service management. We perform a substantial case study of an online conference management system.
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    Program Transformations for Predictable Cache Behavior
    (2009-05-25T06:47:26Z) HUYNH, Bach Khoa; JU, Lei; CHATTOPADHYAY, Sudipta; ROYCHOUDHURY, Abhik
    Real-time embedded software developers need to balance the dual (and seemingly conflicting) concerns of efficiency and predictability. Efficiency concerns are typically addressed by tuning the application and its underlying processing platform through a variety of techniques such as generating custom instructions in the instruction set, or configuring the processing platform. However, timing predictability remains a difficult goal to achieve, specifically in the presence of performance-enhancing micro-architectural features such as data caches. Presence of data caches can cause vast variation in the execution time for even programs with a single path. In this paper, we study a new approach to achieve predictable cache behavior (without large performance degradation) in data-intensive embedded applications. Our approach is to rewrite a given application into a “cache-efficient” style, where the data memory accesses are tracked and transformed to systematically reduce data cache conflicts. Our program transformation leads to lesser execution time variation in the transformed program (across program inputs as well as across cache configurations). We also develop a new Worst-case Execution Time (WCET) analysis method for data caches, and show that it leads to tighter WCET estimates for cache-efficient programs. Our experiments indicate that adopting the cache-efficient style of programming for data-intensive embedded software can help balance the dual concerns of efficiency and predictability.
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    Safety Proofs of Presistence Analysis
    (2010-10-28T03:45:30Z) HUYNH, Bach Khoa; JU, Lei; ROYCHOUDHURY, Abhik
    Caches are widely used in modern computer systems to bridge the increasing gap between processor speed and memory access time. On the other hand, the presence of caches, especially data caches, complicates the static worst case execution time (WCET) analysis. Correctness and tightness of WCET estimates are of crucial importance for system level design of embedded systems. In this report, we show that the originally proposed persistence analysis is both unsafe and pessimistic for worst-case cache behavior modeling.We propose a new update and join functions for persistence analysis and prove their soundness. Furthermore, we extend the semantics of memory block persistence, and propose a scope-aware persistence analysis which combines access pattern analysis and abstract interpretation. The dynamic behavior of a memory access is captured by its temporal scope (the loop iterations where a given memory block is accessed for a given data reference) during address analysis. Temporal scopes as well as loop hierarchy structure (the static scopes) are integrated and utilized to achieve a more precise abstract cache state modeling. We also prove the correctness of the proposed new persistence analysis.
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    Schedulability Analysis of MSC-based System Models
    (2007-10-23T01:40:39Z) JU, Lei; ROYCHOUDHURY, Abhik; CHAKRABORTY, Samarjit
    Message Sequence Charts (MSCs) are widely used for describing interaction scenarios between the components of a distributed system. Consequently, worst-case response time estimation and schedulability analysis of MSC-based speci.-cations form natural building blocks for designing distributed real-time systems. However, currently there exists a large gap between the timing and quantitative performance analysis techniques that exist in the real-time systems literature, and the modeling/speci.cation techniques that are advocated by the formal methods community. As a result, although a number of schedulability analysis techniques are known for a variety of task graph-based models, it is not clear if they can be used to effectively analyze standard speci.cation formalisms such as MSCs. In this work, we make an attempt to bridge this gap by proposing a schedulability analysis technique for MSC-based system speci.cations. We show that compared to existing timing analysis techniques for distributed real-time systems, our pro-posed analysis gives tighter results, which immediately translate to better system design and improved resource dimensioning. We illustrate the details of our analy-sis using a setup from the automotive electronics domain, which consist of two real-life application programs (that are naturally modeled using MSCs) running on a platform consisting of multiple electronic control units (ECUs) connected via a FlexRay bus.
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    Tenant Onboarding in Evolving Multi-tenant SaaS
    (2011-10-06T02:00:53Z) JU, Lei; SENGUPTA, Bikram; ROYCHOUDHURY, Abhik
    A multi-tenant software as a service (SaaS) system has to meet the needs of several tenant organizations, which connect to the system to utilize its services. To leverage economies of scale through re-use, a SaaS vendor would, in general, like to drive commonality amongst the requirements across tenants. However, many tenants will also come with some custom requirements that may be a pre-requisite for them to adopt the SaaS system. These requirements then need to be addressed by evolving the SaaS system in a controlled manner, while still supporting the requirements of existing tenants. In this paper, we study the challenges associated with engineering multi-tenant SaaS systems and develop a framework to help evolve such systems in a systematic manner. We adopt an intuitive formal model of services that is easily amenable to tenant requirement analysis and provides a robust way to support multiple tenant onboarding. We perform a substantial case study of a multi-tenant blog server to demonstrate the benefits of our proposed approach.