Year: 2014

Back in Prague

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I am now back from my two month research visit at Airbus Group Innovations. During my stay, I primarily worked on two things:

  1. Performance analysis of memory accesses in two COTS multi-core platforms. My work extended existing analysis to include the configuration of the memory controller. In particular, the existing setup was improved to enable evaluation of rank-level parallelism within a memory controller, channel parallelism between memory controllers, and different mapping options of cores to memory channels.
  2. I familiarized myself with the certification process for the avionics domain by reading and discussing key standardization documents, e.g. DO-178C for software certification, DO-254 for hardware certification, and DO-297 for integrated modular avionics. I also read several position papers from the Certification Authorities Software Team, most importantly about partitioning guidelines and certification of dual-core platforms. Lastly, I read the ARINC 653 standard, which details the application interface commonly used in avionics systems.

Thanks to Jan Nowotsch and Stefan Schneele for making the visit possible and to my office mates for providing a fun environment to work and learn in.

Paper Accepted at PDP 2015

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Today, we congratulate Hazem Ali for having a paper accepted at PDP 2015. The paper is entitled “Generalized Extraction of Real-Time Parameters for Homogeneous Synchronous Dataflow Graphs” and proposes a heuristic methodology for extracting real-time parameters, such as periods, deadlines and offsets, for applications specified as homogeneous synchronous data-flow (HSDF) graphs. The benefit of the approach is that it enables HSDF applications to be analyzed using traditional real-time techniques and scheduled with common real-time schedulers, such as earliest-deadline first.

Memory Team has Two Papers Accepted at DATE 2015

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The notifications from the DATE conference are in and the Memory Team scores 2 out of 2, just like in 2014. The first paper entitled “A Generic, Scalable and Globally Arbitrated Memory Tree for Shared DRAM Access in Real-Time Systems” was first-authored by Manil and is a collaboration with Jamie Garside and Neil Audsley from University of York. The paper proposes a memory interconnect for shared memory architectures in many-core systems. A main architectural feature is that the interconnect is heavily pipelined enabling it to be synthesized at high frequencies even with a large number of clients. Another highlight is that it has global arbitration that can be programmed to behave like several different arbitration mechanisms, such as TDM, CCSP and FBSP.

The second paper “Retention Time Measurements and Modelling of Bit Error Rates of WIDE I/O DRAM in MPSoCs”was first-authored by our colleagues at Kaiserslautern University of Technology in collaboration with Sven Goossens from our Memory Team. This paper looks into the thermal behavior of 3D-stacked WIDE I/O DRAM and compares its impact on retention time and bit error rates to conventional 2D DRAM chips.

Visiting Researcher at Airbus Group Innovations

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Today, I start a two month stay as Visiting Researcher at Airbus Group Innovations in Ottobrunn, Germany. I will be working together with Jan Nowotsch on topics related to performance analysis of memory accesses in COTS multi-core platforms. During my stay, I look forward to meeting new people learning more about real-time systems in the avionics domain.

DRAMPower v4.0 Released!

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A new version of the DRAMPower tool has been released. The two main features of version 4 are:

  1. DRAMPower can now be compiled as a library. This enables a user to access the tool through an API and log commands and their corresponding time stamps, removing the need to store large command traces on disk. The key benefit of this feature is that users can easily integrate DRAMPower into their own memory controller simulators and obtain power and energy consumption estimates. In fact, this version of DRAMPower is already integrated into the memory controller of the gem5 simulator system and is provided with the latest release.
  2. Improved robustness. The latest build is checked out every night on a test server, compiled, and tested to verify that the output matches an expected reference for a battery of tests. The code is also compiled with a large number of warning flags enabled and treats all warnings as errors. This feature makes it easier for the community to reliably contribute to the tool, which is now possible through github.

Check it out the new version of DRAMPower here.

First PhD Student Graduates From the Memory Team

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Today, Karthik Chandrasekar was promoted to doctor as he confidently defended his PhD thesis “High-Level Power Estimation and Optimization of DRAMs”. The thesis proposes a high-level power estimation tool called DRAMPowerthat estimates the power and energy consumption of different generations of DRAMs based on a memory command trace and current values from the memory datasheet. Since current numbers in datasheets are often pessimistic for a majority of the manufactured memory devices, a methodology is also proposed to characterize DRAM modules post-manufacturing to achieve more accurate power and performance estimates for the characterized devices. Lastly, the thesis discusses power optimization in the context of real-time memory controllers and proposes two power-down strategies to reduce the power consumption of memories in real-time systems without sacrificing worst-case performance.

The defense went very well and the committee was particularly pleased with how the DRAMPower tool was verified using measurements on real hardware and how it has attracted interest from industry. Karthik is the first PhD student to graduate from the Memory Team and the rest of the team wishes him all the best for his future career at Nvidia.

Article in ACM Transactions on Embedded Computing Systems (TECS)

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Manil Dev Gomony just had his first journal article accepted in ACM Transactions on Embedded Computing Systems. The article is entitled “A Real-Time Multi-Channel Memory Controller and Optimal Mapping of Memory Clients to Memory Channels” and is an extension of his DATE paper from 2013, which was the first paper to provide architectures and techniques for multi-channel memory controllers in real-time systems.

The two main contributions of the article are: 1) A configurable real-time multi-channel memory controller architecture with a novel method for logical-to-physical address translation. 2) Two design-time methods to map memory clients to the memory channels, one an optimal algorithm based on an integer programming formulation of the mapping problem, and the other a fast heuristic algorithm. The mapping algorithms are experimentally evaluated, showing benefits over two state-of-the-art mapping algorithms. Finally, a case study is presented that demonstrates how to configure a Wide IO DRAM in a High-Definition (HD) video and graphics processing system to emphasize the practical applicability and effectiveness of the work.

Article in Real-Time Systems Journal has Appeared

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A journal article entitled “Unified overhead-aware schedulability analysis for slot-based task-splitting” has appeared in Real-Time Systems Journal. This article was first-authored by Paulo Baltarejo Sousa during my time at CISTER-ISEP Research Unit in Porto, Portugal and is the result of a collaboration from that time.

The main contribution of the article is a unified scheduling theory for two state-of-the-art slot-based semi-partitioned algorithms, S-EKG and NPS-F. This new theory is based on exact schedulability tests, thus also overcoming many sources of pessimism in existing analyses. Another benefit of the proposed analysis is that it captures overheads, such as interrupts, context switches, and caches, occurring when tasks are deployed on real multi-core platforms. Together, these advantages results in a new efficient and reliable schedulability analysis for slot-based task-splitting algorithms.

RTMemController v1.0 Released

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The Memory Team is proud to release another open-source tool to the community. This tool is called RTMemController and contains a mathematical formalization of the dynamic command scheduler introduced in Yonghui Li’s paper Dynamic Command Scheduling for Real-Time Memory Controllers that will be presented at ECRTS. The tool is capable of determining worst-case and average-case execution times of memory transactions of different transaction sizes and with varying degrees of bank interleaving.

An important driver for releasing this tool is to promote transparency and fair comparisons between work in the field. Longer term development plans for the tool may involve adding support for a memory controller front-end with different transaction schedulers, adding support for more memory generations (currently DDR3 is supported), and making the output compatible with DRAMPower to enable chaining the tools.

The official website of RTMemController is found here. Also check out the paper that describes the scheduling algorithm and its formalization.

Paper Accepted at ECRTS

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Today, we congratulate Yonghui Li on an accepted paper at ECRTS. The paper is entitled Dynamic Command Scheduling for Real-Time Memory Controllers and presents both an architecture and analysis for a dynamically scheduled SDRAM controller supporting different transaction sizes and memory map configurations. This is Yonghui’s first accepted paper and we are proud to see that it got very good reviews from one of the most competitive conferences in the field. Now the work begins on preparing a camera-ready version and making the scheduling algorithm publicly available for comparisons in community.