Counter-Based Approaches for Efficient WCET Analysis of Multicore Processors with Shared Caches

Yiqiang Ding,Wei Zhang 한국정보과학회 2013 Journal of Computing Science and Engineering Vol.7 No.4

To enable hard real-time systems to take advantage of multicore processors, it is crucial to obtain the worst-case execution time (WCET) for programs running on multicore processors. However, this is challenging and complicated due to the inter-thread interferences from the shared resources in a multicore processor. Recent research used the combined cache conflict graph (CCCG) to model and compute the worst-case inter-thread interferences on a shared L2 cache in a multicore processor, which is called the CCCG-based approach in this paper. Although it can compute the WCET safely and accurately, its computational complexity is exponential and prohibitive for a large number of cores. In this paper, we propose three counter-based approaches to significantly reduce the complexity of the multicore WCET analysis, while achieving absolute safety with tightness close to the CCCG-based approach. The basic counter-based approach simply counts the worst-case number of cache line blocks mapped to a cache set of a shared L2 cache from all the concurrent threads, and compares it with the associativity of the cache set to compute the worst-case cache behavior. The enhanced counter-based approach uses techniques to enhance the accuracy of calculating the counters. The hybrid counter-based approach combines the enhanced counter-based approach and the CCCG-based approach to further improve the tightness of analysis without significantly increasing the complexity. Our experiments on a 4-core processor indicate that the enhanced counter-based approach overestimates the WCET by 14% on average compared to the CCCG-based approach, while its averaged running time is less than 1/380 that of the CCCG-based approach. The hybrid approach reduces the overestimation to only 2.65%, while its running time is less than 1/150 that of the CCCG-based approach on average.

Multicore Real-Time Scheduling to Reduce Inter-Thread Cache Interferences

Yiqiang Ding,Wei Zhang 한국정보과학회 2013 Journal of Computing Science and Engineering Vol.7 No.1

The worst-case execution time (WCET) of each real-time task in multicore processors with shared caches can be significantly affected by inter-thread cache interferences. The worst-case inter-thread cache interferences are dependent on how tasks are scheduled to run on different cores. Therefore, there is a circular dependence between real-time task scheduling, the worst-case inter-thread cache interferences, and WCET in multicore processors, which is not the case for single-core processors. To address this challenging problem, we present an offline real-time scheduling approach for multicore processors by considering the worst-case inter-thread interferences on shared L2 caches. Our scheduling approach uses a greedy heuristic to generate safe schedules while minimizing the worst-case inter-thread shared L2 cache interferences and WCET. The experimental results demonstrate that the proposed approach can reduce the utilization of the resulting schedule by about 12% on average compared to the cyclic multicore scheduling approaches in our theoretical model. Our evaluation indicates that the enhanced scheduling approach is more likely to generate feasible and safe schedules with stricter timing constraints in multicore real-time systems.

Numerical Study on the Influence of the Width of the SBM Disc Cutter on Rock Breaking

Yiqiang Kang,Yang-shuai Shu,Li-yun Yang,Ren-shu Yang,Yi-chuan Xu,Zheng Xie,Ke-yao Ren 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.9

The study of the rock-breaking pattern of shaft boring machine (SBM) cutters is the basis for cutter design. In order to reveal the influence of the cutter blade width on the rock-breaking effect, this study established a discrete-continuous coupled rock mass numerical model. By setting different blade widths and types, the variation patterns of cutter forces, rock-breaking area, and specific energy with the blade width were revealed. The influence of the blade type on the breaking coefficient was further quantified according to the fractal dimension. The results show that under the cutting action, the rock mass can be divided into dense core, fractured zone, and elastic deformation zone, with the fractured zones mainly located on the lower side of the cutter's central axis. As the width of the cutter increases, the cutter penetration force and side force increase linearly with the increase in blade width, the breaking area increases and then tends to remain constant, the specific energy decreases first and then increases, and the rock fragmentation factor increases linearly. After scaling the width of the flat blade up to 18 mm and the arc blade to 24 mm, further increase in the blade width does not improve the breaking efficiency but only results in a smaller slag granularity.

Effects of molecular structure of polymeric surfactant on its physico-chemical properties, percolation and enhanced oil recovery

Yiqiang Li,Xin Chen,Zheyu Liu,Ruina Liu,Wentao Liu,Han Zhang 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.101 No.-

Polymeric surfactant can simultaneously thicken aquous phase and reduce water–oil interfacial tension(IFT), which makes it present a great application prospect in the oilfield taword enhanced oil recovery(EOR). There are two kinds of polymeric surfactant with different molecular structures are commonlyused to realize the salt resistance, thermal endurance and shear resistance. However, the influence ofthe molecular structure of polymeric surfactant on their properties related on EOR are not well understood. In the work, we synthesized two kinds of polymeric surfactants with different molecular structurewhich respectively named intermolecular association molecule (IAM) and rigid chain molecule (RCM). Their physico-chemical properties, porous media transportation and EOR are compared with a series ofexperiments. It is found that the hydrodynamic characteristic sizes and retention of IAM are higher thanthose of RCM via the membrane filtration test and nuclear magnetic resonance (NMR) scan. These featuresmake IAM have a larger resistance factor and residual resistance factor than RCM and hydrolyzedpolyacrylamide (HPAM) in the same viscosity. Compare to HPAM with shear thinning, RCM presents aNewtonian fluid region and IAM presents a shear thickening region when the shear rate is lower than1 s 1. The spatial structure of IAM can pack oil drop into its network, which make it easy to form oilin-water-in-oil (O/W/O) emulsions. Moreover, the concentration and water–oil ratio (WOR) rarely affectthe stability of IAM emulsions once the intermolecular association generated. The increamental oil recoveryfactor of IAM is 17.5% after water flooding in the three-layer core flooding experiments with the permeabilityof 500 mD, 1500 mD and 3000 mD at 55℃, which is higher than that of 14.5% for RCM and11.4% for HPAM.

清華簡《厚父》疏證

Yiqiang Wu 한국중국학회 2017 中國學報 Vol.81 No.-

Through the study of the literature itself of “Hou Fu”(厚父), from the aspects of words, sentence and meaning, the original text has been carefully explained and dredged. The interpretation of some key words, such as gong(鞏), you(佑), chuan(傳), yuan(淵), zuo(佐) etc, I have submitted my opinions in the explanation of some words and the understanding of several characters, Such as the interpretation of kong jia(孔甲), gao tao(皋陶), as well as the interpretation of the identity of “Hou Fu”, It is pointed out that the “Hou Fu” may be the “Qing fu”(慶輔)of Yu zi(鬻子), the minister of Shang tang(商湯),It enhances the understanding of the literature itself and helps to judge the nature of the text. 清華簡《厚父》,是一篇重要的文獻,全篇爲王與厚父的對話,王通過回顧夏代歷史,總結如何才能永保邦國。厚父則從德、天命、民心、戒酒等幾方面闡明保國之道。整理者以及諸多學者已從字詞、文句等方面做了很好的解釋。筆者在研讀《厚父》過程中,亦有些許看法,今就字詞、斷句、文意及文本屬性等基本方面進行疏通。

Exploiting Static Non-Uniform Cache Architectures for Hard Real-Time Computing

Yiqiang Ding,Wei Zhang 한국정보과학회 2015 Journal of Computing Science and Engineering Vol.9 No.4

High-performance processors using Non-Uniform Cache Architecture (NUCA) are increasingly used to deal with the growing wire delays in multicore/manycore processors. Due to the convergence of high-performance computing with embedded computing, NUCA caches are expected to benefit high-end embedded systems as well. However, for real-time systems that use multicore processors with NUCA caches, it is crucial to bound worst-case execution time (WCET) accurately and safely. In this paper, we developed a WCET analysis approach by considering the effect of static NUCA caches on WCET. We compared the WCET in real-time applications with different topologies of static NUCA caches. Our experimental results demonstrated that the static NUCA cache could improve the worst-case performance of realtime applications using multicore processor compared to the cache with uniform access time.

Genome-wide Transcriptome Profiling Reveals the Mechanism of the Effects of Uniconazole on Root Development in Glycine Max

Yiqiang HAN,Yamei GAO,Ying Shi,Jidao Du,Dianfeng Zheng,Guifeng Liu 한국식물학회 2017 Journal of Plant Biology Vol.60 No.4

Uniconazole, a plant growth retardant, possessesthe ability to improve quality and increase tolerance of plant. However, it is known little about the effects of uniconazoleon root. In this study, uniconazole treatments that were appliedthrough seed soaking, promoted soybean root development,and the microstructure of root showed increase of corticalthickness and cortex cell width. Meanwhile, the endogenoushormone content also altered in root after uniconazoletreatments. To obtain the molecular mechanism underlyingthe effects of uniconazole on root, we performed an RNAseqof roots harvested 3 days after uniconazole treatment. Through analyses of phytohormone-associated genes forendogenous hormones changes, we found that not only GAbiosynthesis pathway but also the regulation genes of thepathway were affected. Above all, the dominant pathwayplant hormone signal transduction may be the main factor ofthe cambium proliferation, in especial ethylene/ERF signalingpathway. Moreover, the transcriptome demonstrated differentiallyexpressed genes that determined cell division and cell wallmodification may be regulators of root growth. CLE signalingand receptor-like kinases may play a crucial role in the rootelongation. Besides, 177 transcription factors (TFs) wereinvolved in response to uniconazole. Taken together, allthese findings provide insights into the complex molecularmechanisms associated with root development after uniconazoletreatment.

Multicore-Aware Code Co-Positioning to Reduce WCET on Dual-Core Processors with Shared Instruction Caches

Yiqiang Ding,Wei Zhang 한국정보과학회 2012 Journal of Computing Science and Engineering Vol.6 No.1

For real-time systems it is important to obtain the accurate worst-case execution time (WCET). Furthermore, how to improve the WCET of applications that run on multicore processors is both significant and challenging as the WCET can be largely affected by the possible inter-core interferences in shared resources such as the shared L2 cache. In order to solve this problem, we propose an innovative approach that adopts a code positioning method to reduce the inter-core L2 cache interferences between the different real-time threads that adaptively run in a multi-core processor by using different strategies. The worst-case-oriented strategy is designed to decrease the worst-case WCET among these threads to as low as possible. The other two strategies aim at reducing the WCET of each thread to almost equal percentage or amount. Our experiments indicate that the proposed multicore-aware code positioning approaches, not only improve the worstcase performance of the real-time threads but also make good tradeoffs between efficiency and fairness for threads that run on multicore platforms.

Bounding Worst-Case DRAM Performance on Multicore Processors

Yiqiang Ding,Lan Wu,Wei Zhang 한국정보과학회 2013 Journal of Computing Science and Engineering Vol.7 No.1

Bounding the worst-case DRAM performance for a real-time application is a challenging problem that is critical for computing worst-case execution time (WCET), especially for multicore processors, where the DRAM memory is usually shared by all of the cores. Typically, DRAM commands from consecutive DRAM accesses can be pipelined on DRAM devices according to the spatial locality of the data fetched by them. By considering the effect of DRAM command pipelining, we propose a basic approach to bounding the worst-case DRAM performance. An enhanced approach is proposed to reduce the overestimation from the invalid DRAM access sequences by checking the timing order of the co-running applications on a dual-core processor. Compared with the conservative approach, which assumes that no DRAM command pipelining exists, our experimental results show that the basic approach can bound the WCET more tightly, by 15.73% on average. The experimental results also indicate that the enhanced approach can further improve the tightness of WCET by 4.23% on average as compared to the basic approach.

Flame retardancy and thermal degradation behavior of red gum wood treated with hydrate magnesium chloride

Yiqiang Wu,Chunhua Yao,Yunchu Hu,Shoulu Yang,Yan Qing,Qinglin Wu 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5

Flame retardancy and thermal degradation of wood treated with magnesium chloride (MgCl2 6H2O) were investigated. Results showed that MgCl2 6H2O decreased flame intensity and heat release rate, and reduced smoke concentration and gas yield. From ambient temperature to 250 ℃, MgCl2 6H2O reduced wood combustibility by gas dilution mechanism. The chemical started to decompose at 350 8C and produced MgOHCl, in which -Cl and -Mg free radicals were generated and intervened the chain reactions of wood combustion. Hydrogen chloride gas generated promoted wood charring. MgCl2 6H2O gradually converted to MgOHCl and MgO compounds at higher temperatures, and MgO suppressed wood combustion by the wall effect mechanism.