Changes

== Lab 4 6 ==

* Digital sound is typically represented, uncompressed, as signed 16-bit integer signal samples. There is 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 per second per channel, for a total of 88.2 or 96 thousand samples per second (kHz). 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).

=== Basic Sound Scale Program Three Approaches ===

Get the files for Three approaches to this lab on one of the [[SPO600 Servers]] -- but you can perform the lab wherever you want.problem are provided:

# Unpack the archive The basic or Naive algorithm (<code>/public/spo600-algorithm-selection-labvol1.tgzc</code>). This approach multiplies each sound sample by 0.75, casting from signed 16-bit integer to floating point and back again. Casting between integer and floating point can be [[Expensive|expensive]] operations.# Examine the A lookup-based algorithm (<code>vol1vol2.c</code> source code). This program:approach uses a pre-calculated table of all 65536 possible results, and looks up each sample in that table instead of multiplying.## Creates 5,000,000 random "sound samples" in a data array A fixed-point algorithm (the number of samples is set in the <code>volvol3.hc</code> file).## Scales those samples by the volume factor 0.75 This approach uses fixed-point math and stores them back bit shifting to perform the data arraymultiplication without using floating-point math.## Sums the output array and prints the sum. '''(Why is this important?)'''# Build and test this file.#* Does it produce the same output each time?# Test the performance of this program. '''Adjust the number of samples as necessary to get measurable results'''.#* How long does it take to run the scaling?#* How much time is spent scaling the sound samples? Be sure to eliminate the time taken for the non-scaling part of the program (e.g., random sample generation). === Don'''(How will you do this?)'''#* 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?t Compare Across Machines ===

Try these alternate algorithms Get the files for scaling this lab from one of the sound samples by modifying copies of <code>vol1.c</code>. Edit [[SPO600 Servers]] -- but you can perform the <code>Makefile</code> lab wherever you want (feel free to build use your modified programs as well as the originallaptop or home system). Test each approach to see the performance impact:on both an x86_64 and an AArch64 system.

Review the contents of this archive:* <code>vol.h</code> controls the number of samples to be processed* <code>vol1.c</code>, <code>vol2.c</code>, and <code>vol3.c</code> implement the various algorithms* The <code>Makefile</code> can be used to build the programs Perform these steps:# PreUnpack the archive <code>/public/spo600-calculate algorithm-selection-lab.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 the relative performance of each scaling algorithm.# Build and test each of the programs.#* Do all possible sample values multiplied by of the algorithms produce the volume factorsame output?#** How can you verify this?#** If there is a difference, and look up is it significant enough to matter?#* Change the number of samples so that each sample in that table program takes a reasonable amount of time to get execute (suggested minimum 20 seconds, 1 minute or more is better).# Test the scaled valuesperformance of each program.# Convert * Find a way to measure performance ''without'' the volume factor 0.75 time taken to a fixperform the test setup pre-point integer by multiplying by a binary number representing a fixedprocessing (generating the samples) and post-point value "1". For example, you could use 0b100000000 processing (= 256 in decimalsumming the results) so that you can measure ''only'' the time taken to represent 1scale the samples.00, and therefore use 0.75 '''This is the hard part!'''#* How much time is spent scaling the sound samples?#* 256 = 192 for your volume factor. Multiply Do multiple runs take the same time? How much variation do you observe? What is the likely cause of this fixed-point integer volume factor variation?#* Is there any difference in the results produced by each sample, then shift the result to various algorithms?#* Does the right difference between the required number of bits after algorithms vary depending on the multiplication (>>8 if architecture and implementation on which you're using 256 as test?#* What is the multiplier).relative memory usage of each program?# Was your prediction accurate?

Blog about your experiments with a detailed analysis of your results, including memory usage, time performance, accuracy, and trade-offs.

ImportantMake sure you convincingly prove your results to your reader! -- 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 on AArchie against another 64-bit ARM system such as the various class servers, or between the class servers and a Raspberry Pi 3 (in 64-bit mode) or an ARM Chromebook.* For x86_64, you could compare the performance of different processors, such as xerxes, your own laptop or desktop, and Seneca systems such as Matrix, Zenit, or lab desktops.

* 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 in the code under test function only -- you need to be able to remove the rest of the processing time from your evaluation.* You may need to run a very large amount of sample data through the function to be able to detect its performance. Feel free to edit the sample count in <code>vol.h</code> as necessary.

* Be aware of what other tasks the system is handling during your test run, including software running on behalf of other users.

==== Analyzing Results =Tips ===* What is the impact {{Admon/tip|Analysis|Do a thorough analysis of various optimization levels on the software performance? results. Be certain (For example, compiling with -O0 / -O1 / -O2 / -O3and prove!)* Does that your performance measurement ''does not'' include the distribution generation or summarization of the test data matter? (e.gDo multiple runs and discard the outliers.Decide whether to use mean, is there any difference if there are no absolute large numbersminimum, or no negative numbers?)* If samples are fed at CD rate (44100 samples per second x 2 channels x 2 bytes per sample), can each of maximum time values from the algorithms keep up?* What is the memory footprint of each approach?* What is the performance of each approach?* What is the energy consumption of each approach? (What information do you need to calculate this?)* Various machines within an architecture have very different performance profiles, energy consumptionmultiple runs, and hardware costs -- so it's not reasonable to compare explain why you made that decision. Control your variables well. Show relative performance between machinesas percentage change, but it is reasonable to compare the relative performance of the algorithms in each contexte.g. Does the ratio of performance of the various approaches remain constant across the machines? Why or why not?* What other optimizations can be applied to , "this problem?approach was NN% faster than that approach".}}

Another 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|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 (and preferred) approach, as used in the provided sample code: allocate the array space with <code>malloc()</code> or <code>calloc()</code>bit signed 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!}}