Lab-1: Profiling/Optimizing Video Decoder Using ADS. National Chiao Tung University Chun-Jen Tsai 3/3/2011

Transcription

1 Lab-1: Profiling/Optimizing Video Decoder Using ADS National Chiao Tung University Chun-Jen Tsai 3/3/2011

2 Profiling MPEG-4 SP Decoder Goal: Profiling and optimizing the MPEG-4 video decoder, m4v_dec Tasks: Profile the video decoder under ADS Analyze the results and identify the hotspots Optimize the decoder based on the hotspot analysis Redraw the pie charts after your optimization Please also write a report (two-column, no cover sheet, 4 pages at most) to summarize your analysis and optimization of the system model 2/22

3 Embedded Software Design Flow Take ARM-based systems for example: *.c/.cpp C/C++ source C libraries *.s asm source C compiler assembler linker *.o ELF object file Librarian *.axf image System models axd debug object libraries ARMulator development board All the tools are integrated in the IDE: ARM Developers Suite (ADS) 3/22

4 Generations of ARM Toolchains ARM SDT Software Development Tools Final version 2.5, 1998 ARM ADS ARM Software Development Suite Final version 1.2, 2000 Still popular in the industry ARM RVDS RealView Development Suite Latest version 4.0 With emphasis on Electronic System Level (ESL) design environment 4/22

5 Cross-Platform Development Host Computer serial, Ethernet, or JTAG cable ADS IDE environment Development board You can obtain a 45-day full function ADS 1.2 trial CD image from the TA A tutorial can be downloaded from 5/22

6 Verification of Your Software During the development cycle, you often have to debug your software; for embedded firmware development, the process involves three components: Debugger (runs on host computer): axd Debug agent: interface between debugger and your code Target platform: the platform (simulated or emulated) that executes your code 6/22

7 Debug Agent A debug agent performs the actions requested by the debugger, for example: setting breakpoints reading from memory writing to memory. The debug agent is not the program being debugged, or the debugger itself Examples: Angel, JTAG circuits 7/22

8 Target Platform Target platform can be real hardware or simulator If simulator platform is used, the core component is a instruction set simulator (ISS) For example, ARMulator is the famous simulator in ARM ADS ARMulator also doubles as a platform simulator, but not as powerful as simulators from other venders (such as CoWare) 8/22

9 ARM Debugging Setup Runs on PC Host Probably runs on the same PC Host AXD and armsd Debuggers Guide, Page /22

10 ADS Workspace project window source window build messages 10/22

11 AXD Desktop System view source window disassembly window Console system output 11/22

12 Profiling and CPU Cycle Analysis Profiling and CPU cycle analysis are two different approaches to analyze your software Profiling gives you a per-function complexity analysis CPU cycle analysis gives you more insights into the software regarding computation vs. memory accesses Under ADS, you use AXD to do both For profiling, ADS generates some data and a command line toolarmprof is used to analyze data For cycle analysis you must display ARMulator internal statistics counter in an ADS window 12/22

13 CPU Cycle Types of ARM Sequential (S cycle) The ARM core requests a transfer to or from an address which is either the same, or one word or one-half-word greater than the preceding address. Non-sequential (N cycle) The ARM core requests a transfer to or from an address which is unrelated to the address used in the preceding address. Internal (I cycle) The ARM core does not require a transfer, as it performing an internal function, and no useful prefetching can be performed at the same time Coprocessor register transfer (C cycle) The ARM core wished to use the data bus to communicate with a coprocessor, but does not require any action by the memory system. 13/22

14 The System Model Used in Labs For labs, we will use m4v_dec an MPEG-4 video decoder, as the system model Contains 28 files, 5212 lines of C code Differences between m4v_dec and xvid 0.9: Simpler API Support for Simple Profile combined mode with resync marker Decoder-only library Pure C implementation (thus, can be used as a system model) m4v_dec is based on version 0.9 of the GNU MPEG-4 codec project, xvid (see for latest xvid source). 14/22

15 About the Source Package There are two project files in the project directory, m4v_dec : m4v_dec.mcp is the project workspace file for ADS; doubleclick this and ADS will bring up the Development IDE Makefile is the make file for ecos/gcc toolchain In the tools directory, there is a Win32 program, vidview.exe, for playing the decoded video (output.yuv) In the bitstream directory, there is a sample compressed video bitstream, foreman_150.m4v 15/22

16 Video Decoder Block Diagram The functional block diagram of m4v_dec: video bitstream DCT coefficient data N decoded image To output (display) VLD DC/AC Q -1 IDCT Y -1 Use MC? + macroblock mode, motion vector MC VLD: variable length decoding DC/AC 1 : inverse DC/AC prediction Q 1 : inverse quantization IDCT: inverse transform MC: motion compensation Bilinear: half-pel Interpolation Bilinear reference image 16/22

17 About Optimization A sample result of profiling is as follows IDCT Inverse Quantization Interpolation Boundary Extension Color Conversion Motion Compensation DC/AC Prediction VLC Decoding Obviously, for optimization you want to start with theidct() function inidct.c 17/22

18 Main Decoder Modules You may want to take a deeper look of the following files: bilinear8x8.c (interpolation) idct.c (inverse DCT) mbcoding.c (VLC decoding) quant_h263.c (inverse quantization) mem_transfer.c (motion compensation) mbprediction.c (DC/AC prediction) 18/22

19 Hint: Removing Floating Point Floating point operations in general can be removed as follows: main(int argc, char **argv) { double a, b; int c; main(int argc, char **argv) { int a, b; int c; } a = ; b = ; c = (int) floor(a+b+0.5); } a = 6434; // 2048* b = 2896; // 2048* c = (a+b+1024)>>11; 19/22

20 After Removing FP Operations An example of optimized result: IDCT Inverse Quantization Interpolation Boundary Extension Color Conversion Motion Compensation DC/AC Prediction VLC Decoding 20/22

21 Necessary Charts in Your Report In your report, you shall provide the following information Draw a pie chart that shows major CPU load distribution among functions For the top-10 functions which consume most CPU time, draw a pie chart to show the distribution of memory cycles 21/22

22 References for This Lab You can find some pdf ebooks related to this lab in the document folder of your ADS installation directory: For General ARM Programming ADS Programming Guide (includes three manuals) Writing Efficient C for ARM (ARM App. Note 34) For Profiling using AXD AXD and armsd Debuggers Guide For Using ARMulator ADS Debug Target Guide Benchmarking with ARMulator (ARM App. Note 93) The ARMulator Configuration File (ARM App. Note 52) For MPEG-4 Video Decoder Knowledge Class slides Google or Wikipedia 22/22