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On Workload in an SCA-based System, with Varying Component and Data Packet Sizes Tore Ulversøy 1 Jon Olavsson Neset 2 1 FFI 1 UNIK University Graduate.

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Presentation on theme: "On Workload in an SCA-based System, with Varying Component and Data Packet Sizes Tore Ulversøy 1 Jon Olavsson Neset 2 1 FFI 1 UNIK University Graduate."— Presentation transcript:

1 On Workload in an SCA-based System, with Varying Component and Data Packet Sizes Tore Ulversøy 1 Jon Olavsson Neset 2 1 FFI 1 UNIK University Graduate Center 1 University of Oslo (UiO) 2 Norwegian University of Science and Technology (NTNU)

2 Outline Background and Problem Definition Empirical Analysis Analysis using Low-Complexity Analytical Models Conclusions

3 Background The base code of one of the waveform applications used in the following originate from a member in, and the waveform application is also used for other activities in The Regular Task Group on SDR founded below the RTO-IST-080 RTO-IST-080 RTG-038 Software Defined Radio currently, the team consists of experts from government, university and industry from CA, DK, GE, HU, IT, NL, NO, SP, TU, US and: SDR Forum headed by NL (Chairman: Hans Segers, TNO)

4 Background: Main Objectives of RTG- 038 © IBM/Levono © Rockwell Collins … 011010 … © Spectrum Signal Processing Share knowledge & experience of (multi)national SDR/SCA developments Report on possibilities of sharing waveforms and waveform components Investigations of portability and interoperability: SCA-based implementation of STANAG 4285 waveform demonstrate portability onto national SDR platforms demonstrate interoperability between the different implementations 1. 2. 3.

5 Problem Definition and Problem Background SCA defines an environment that allows applications to be built as compositions of SW components (and devices) SCA defines a distributed system, communication through CORBA for CORBA- capable processors There is wide freedom as to how small components to split the application into: Many small components reuse of components becomes easier, but CPU overhead increases What are the CPU overhead effects of a fine structure (many components) relative to a course one (few components), and how can we predict this overhead? C_tot

6 Analysis Approach: CPU workload implied by a task or a group of tasks = the fraction of available processor cycles occupied over a time period

7 Empirical Analysis Using OSSIE (Open Source SCA Implementation Embedded) [2] from VirginiaTech which uses omniORB [3] –Advantages: Low user-threshold, full source-code available, Linux-based Profiling and monitoring tools: –OProfile [4] –SYSSTAT sar [5]

8 Empirical Analysis, Simple Waveform Application Stanag 4285, TX part. Base code provided by Telefunken Racoms for RTO-IST-080 RTG-038 Implemented as three different configurations, all performing the same processing functional work Non-SCA c version as a reference Packet rate regulator

9 Empirical Analysis, Stanag 4285 TX: Results, User WL measured by SYSSTAT sar (sar –u 40 5)

10 Empirical Analysis, Stanag 4285 TX: Results, User+System WL measured by SYSSTAT sar (sar –u 40 5)

11 Empirical Analysis, Synthetic Application A total of 9 FIR-filters, N taps and packet size B (NxB mult/adds per FIR) Both N and B can be varied 4 different configurations c version as a reference Packet rate regulator

12 Synthetic Application: WL versus Configuration and N WL results measured by SYSSTAT sar (sar –u 40 3)

13 Synthetic Application: WL versus Packet Size Packet rate: 10/sec N and B selected such that C implementation (FUNC) is at 10±0,3% user CPU WL WL overhead is seen to increase significantly with B

14 The Simple Lower Bound Model (SLBM) Ideal, unrealistically optimistic model Serves as a lower bound t i = number of cycles per packet CNCN C N+1

15 Parameters in the Simple Lower Bound Model For simplicity, we measure the parameters in the model with OProfile and/or SYSSTAT sar, using test applications: for (i=0; i < BLSZ; i++)...... c-prog CORBA test application:

16 Results, SLBM The simple model describes the dominating part of the user CPU overhead. Agreement best for small packet sizes Packet Size N and B selected such that C implementation (FUNC) is at 10±0,3% user CPU WL Measured SLBM M=11, Packet rate =10/sec

17 The Context Switch Model (CSM) Context Switch Rate [switches/second] CS Direct Cost [cycles] Cycle rate of the processor CS Indirect Cost [cycles] Here: Using course estimate based on addressed space and memory speed Here: 5µsec = 9300 cycles Measured 1300 for example next page

18 Results, CSM With the CS model, we better explain the measured WL Measured CSM, only t CSD, course estimate CSM example (course parameter estimates) M=11, Packet rate =10/sec N and B selected such that C implementation (FUNC) is at 10±0,3% user CPU WL Packet Size

19 Conclusions: We have used empirical analysis and simple analytical models to understand the effects of granularity in an SCA-based system w/CORBA capable processors When executing the same total functional processing work, we observe that the processor workload increases as the number of components increases This overhead increases with data packet size, and becomes more dominant the lesser the functional work per packet Contributors: Data conversions, packet communication through CORBA, direct cost of context switches, indirect cost of context switches Hence the scalability and reusability benefits that result from implementing the SDR-application with a high number of components, must be balanced against the processing efficiency loss that occurs when having to run several components on the same processor Two simple models are described that help explain the major effects, and may be used to calculate the overhead

20 References: [1] P. J. Fortier and H. E. Michel, Computer Systems Performance Evaluation and Prediction. Amsterdam: Digital Press, 2003. [2] VirginiaTech, OSSIE development site for software-defined radio, http://ossie.wireless.vt.edu/trac as of Dec. 20 2007 [3] omniORB, http://omniorb.sourceforge.net/ as of Feb. 29 2008 [4] OProfile - A System Profiler for Linux, http://oprofile.sourceforge.net as of Feb. 29 2008 [5] SYSSTAT, http://pagesperso-orange.fr/sebastien.godard/ as of Feb. 29 2008 [6] Chuanpeng Li, Chen Ding, and Kai Shen, "Quantifying The Cost of Context Switch," in ExpCS '07: Proceedings of the 2007 workshop on Experimental computer science, San Diego, CA, 13-14 June 2007.

21 Questions?


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