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[[Category:SPO600 Labs- Retired]]{{Admon/lab|Purpose of this Lab|In this lab, you will select one investigate the impact of two different algorithms for adjusting which produce the volume of PCM audio samples based same effect.}}{{Admon/important|x86_64 and AArch64 Systems|This lab must be performed on benchmarking of two possible approachesboth x86_64 and AArch64 systems. You may use the [[SPO600 Servers]] or you may use other system(s) -- it might make sense to use your own x86_64 system and [[SPO600_Servers#AArch64:_israel.cdot.systems|israel.cdot.systems]] for AArch64.}}
== Lab 5 ==
=== Background ===
* Digital sound is typically represented, uncompressed, as signed 16-bit integer signal samples. There is one stream are two streams of samples , one each for the left and right stereo channels, at typical sample rates of 44.1 or 48 thousand samples (kHz)per secondper channel, for a total of 88.2 or 96 thousand samples per second. Since there are 16 bits (2 bytes) per sample, the data rate is 88.2 * 1000 * 2 = 176,400 bytes/second (~172 KiB/sec) or 96 * 1000 * 2 = 192,000 bytes/second (~187.5 KiB/sec).* To change the volume of sound, each sample can be scaled (multiplied) by a volume factor, in the range of 0.00 (silence) to 1.00 (full volume).
* On a mobile device, the amount of processing required to scale sound will affect battery life.
=== Basic Sound Scale Program Multiple Approaches ===
These are the six programs: # Unpack vol0.c is the archive <code>/public/spo600-20181-basic or naive algorithm. This approach multiplies each sound sample by the volume scaling factor, casting from signed 16-selection-labbit integer to floating point and back again. Casting between integer and floating point can be [[Expensive|expensive]] operations.tgz</code># Examine the <code>vol1.c</code> source codedoes the math using fixed-point calculations. This program:avoids the overhead of casting between integer and floating point and back again.## Creates 500vol2.c pre-calculates all 65536 different results,000 random "sound samples" in an and then looks up the answer for each input array value.# vol3.c is a dummy program - it doesn't scale the volume at all. It can be used to determine some of the overhead of the rest of the processing (besides scaling the number of samples is set in volume) done by the <code>volother programs.# vol4.h</c uses Single Instruction, Multiple Data (SIMD) instructions accessed through inline assembley (assembly language code> fileinserted into a C program). This program is specific to the AArch64 architecture and will not build for x86_64.## Scales those samples by the volume factor 0vol5.c uses SIMD instructions accessed through Complier Intrinsics. This program is also specific to AArch64. '''Note that vol4.75 c and stores them in an output arrayvol5.c will build only on AArch64 systems because they use architecture-specific SIMD instructions.'''## Sums === Don't Compare Across Machines === In this lab, ''do not'' compare the output array relative performance across different machines, because various systems have different microarchitectures, memory configurations, peripheral implementations, and prints clock speeds, from mobile-class to server-class (e.g. Intel Atom vs. Xeon; AMD APU vs. Threadripper; ARM Cortex-A55 vs. Neoverse-V2). However, ''do'' compare the relative performance of the various algorithms on the sum''same'' machine.# Build === Important! === The hardest part of this lab, and the most critical component, is being able to separate the performance of the volume scaling code from the rest of the code (which only exists to set up the test of the scaling code). The volume scaling code runs ''very'' quickly, and is dwarfed by the rest of the code. You '''must''':* Control variables in your test this fileenvironment.#* Does it produce * What else is the machine doing while you are testing?** Who else is logged in to the machine?** What background operations are being performed?** How does your login on the same output each timemachine affect performance (e.g., network activity)?* <span style="background: # Test ffff00">Isolate the performance of the volume scaling code.</span> This is one of the most important parts of this lab! There are two practical approaches:** Subtract the performance of the dummy version of the program from each of the other versions, or** Add code to the programto measure and report just the performance of the volume-scaling code* Repeat the tests multiple times to ensure that the results you are getting are consistent, valid, and accurately reflect the performance of the volume scaling code. Adjust ** Make sure you are performing enough calculation to give a useful result -- adjust the number SAMPLES value in <code>vol.h</code> to a sufficiently high value** Discard outliers (unusually high or low results)** Average the results.** Take some measure of the amount of samples as necessaryvariation of your results (e.g., tolerance limits or standard deviation). === Resources ===* ARM Aarch64 documentation** [http://developer.arm.com/ ARM Developer Information Centre]*** [https://developer.arm.com/docs/den0024/latest ARM Cortex-A Series Programmer’s Guide for ARMv8-A]*** The ''short'' guide to the ARMv8 instruction set: [https://www.element14.com/community/servlet/JiveServlet/previewBody/41836-102-1-229511/ARM.Reference_Manual.pdf ARMv8 Instruction Set Overview] ("ARM ISA Overview")#* How ** The ''long does it take '' guide to run?the ARMv8 instruction set: [https://developer.arm.com/docs/ddi0487/latest/arm-architecture-reference-manual-armv8-for-armv8-a-architecture-profile ARM Architecture Reference Manual ARMv8, for ARMv8-A architecture profile] ("ARM ARM")** [https://developer.arm.com/docs/ihi0055/latest/procedure-call-standard-for-the-arm-64-bit-architecture Procedure Call Standard for the ARM 64-bit Architecture (AArch64)] * x86_64 Documentation#* How much time is spent scaling * AMD: https://developer.amd.com/resources/developer-guides-manuals/ (see the AMD64 Architecture section, particularly the sound samples?''AMD64 Architecture Programmer’s Manual Volume 3: General Purpose and System Instructions'')** Intel: http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html** Web sites*** http://ref.x86asm.net/*** http://sandpile.org/ * Assembler and Inline Assembler** [[Assembler Basics]]** [[Inline Assembly Language]]** GAS Manual - Using as, The GNU Assembler: https://sourceware.org/binutils/docs/as/#* Do multiple runs take ** Specifically, the same time?[http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/Extended-Asm.html Assembler Instructions with C Expression Operands] section == Benchmarking ==
Perform these steps '''on both x86_64 and AArch64 systems''':# PreUnpack the archive <code>/public/spo600-volume-calculate examples.tgz</code># Study each of the source code files and make sure that you understand what the code is doing.# '''Make a lookup table (array) prediction''' of all possible sample values multiplied by the volume factor, relative performance of each scaling algorithm.# Build and look up test each sample in that table to get of the scaled valuesprograms.# Convert * Do all of the volume factor 0.75 algorithms produce the same output?#** How can you verify this?#** If there is a difference, is it significant enough to a fix-point integer by multiplying by a binary matter?#* Change the number representing of samples so that each program takes a fixed-point value "1"reasonable amount of time to execute (suggested minimum is 20 seconds). For example# Test the performance of each program (vol0 through vol3 on x86_64, you could use 0b100000000 and vol0 through vol5 on AArch64)#* Find a way to measure performance ''without'' the time taken to perform the test setup pre-processing (generating the samples) and post-processing (= 256 in decimalsumming the results) so that you can measure ''only'' the time taken to represent 1scale the samples.00. Shift '''This is the hard part!'''#* How much time is spent scaling the sound samples?#* Do multiple runs take the same time? How much variation do you observe? What is the likely cause of this variation?#* Is there any difference in the results produced by the various algorithms?#* Does the difference between the result to algorithms vary depending on the right architecture and implementation on which you test?#* What is the required number relative memory usage of bits after each program?# See if you can measurably increase performance by changing the multiplication compiler option (via the Makefile)# Was your prediction about performance accurate?# Find all of the questions, marked with <code>'''Q:'''</code>8 if you're using 256 as , in the multiplier)program comments, and answer those questions.
=== Conclusions Deliverables ===Blog about your experiments with an analysis of your results. Do a detailed analysis, including memory usage, time performance, and other trade-offs.
'''Make sure you convincingly <u>prove</u> your results to your reader!''' Re-read the [[#Important.21|section marked ''Important'' above]] and make sure you address the issues explained there. Also be sure to explain what you're doing so that a reader coming across your blog post understands the context (in other words, don't just jump into a discussion of optimization results -- give your post some context). '''Optional - Recommended:''' Compare results across several '''implementations ''' of AArch64 and x86_64 systems. Note that on different CPU implementations, the relative performance of different algorithms will vary; for example, table lookup may outperform other algorithms on a system with a fast memory system (cache), but not on a system with a slower memory system.* For AArch64, you could compare the performance of Cortex-A57 octa-core CPU (on aarchie) AArchie against the APM XGene-1 octa-core CPUs (on bbetty or ccharlie), or against Cortex-A53 cores (e.g., on a Raspberry Pi 34 (in 64-bit mode)or an ARM Chromebook.* For x86_64, you could compare the performance of different processors, such as xerxesportugal.cdot.systems, your own laptop or desktop, and Seneca systems such as Matrix, Zenit, or lap lab desktops.
=== Things to consider ===
==== Design of Your Tests ====
* Most solutions for a problem of this type involve generating a large amount of data in an array, processing that array using the function being evaluated, and then storing that data back into an array. The test setup can take more time than the actual test! Make sure that you measure the time taken for the code in question (the part that scales the test function only sound samples) ONLY -- you need to be able to remove the rest of the processing time from your evaluation.* You may need to run a very massive large amount of sample data through the function to be able to detect its performance. Feel free to edit the sample count in <file>vol.h</file> as necessary.
* If you do not use the output from your calculation (e.g., do something with the output array), the compiler may recognize that, and remove the code you're trying to test. Be sure to process the results in some way so that the optimizer preserves the code you want to test. It is a good idea to calculate some sort of verification value to ensure that both approaches generate the same results.
* Be aware of what other tasks the system is handling during your test run, including software running on behalf of other users. === Tips ==={{Admon/tip|Analysis|Do a thorough analysis of the results. Be certain (and prove!) that your performance measurement ''does not'' include the generation or summarization of the test data. Do multiple runs and discard the outliers. Decide whether to use mean, minimum, or maximum time values from the multiple runs, and explain why you made that decision. Control your variables well. Show relative performance as percentage change, e.g., "this approach was NN% faster than that approach".}}
The version of the <code>time</code> command located in <code>/bin/time</code> gives slightly different information than the version built in to bash -- including maximum resident memory usage: <code>/bin/time ''./programName''</code>}}
{{Admon/tip|SOX|If you want to try this with actual sound samples, you can convert a sound file of your choice to raw 16-bit signed integer PCM data using the [http://sox.sourceforge.net/ sox] utility present on most Linux systems and available for a wide range of platforms.}}
{{Admon/tip|Stack Limitstdint.h|Fixed-size, non-static arrays will be placed in the stack space. The size of the stack space is controlled by per-process limits, inherited from the shell, and adjustable with the <code>ulimitstdint.h</code> command. Allocating an array larger than the stack header provides definitions for many specialized integer size limit will cause a segmentation fault, usually on the first write. To see the current stack limit, use <code>ulimit -s</code> (displayed value is in KB; default is usually 8192 KB or 8 MB)types. To set the current stack limit, place a new size in KB or the keyword Use <code>unlimitedint16_t</code>after the <code>for 16-s</code> argument.<br /><br />Alternate (bit signed integers and preferred) approach, as used in the provided sample code: allocate the array space with <code>malloc()</code> or <code>calloc()uint16_t</code>for 16-bit unsigned integers.}}
{{Admon/tip|stdint.hScripting|The <code>stdint.h</code> header provides definitions for many specialized integer size types. Use <code>int16_t</code> for 16-bit signed integers.bash scripting capabilities to reduce tedious manual steps!}}
