Fall 2014 SPO600 Weekly Schedule
- 1 Summary Table
- 2 Evaluation
- 3 Week 1
- 4 Week 2
- 5 Week 3
- 6 Week 4
- 7 Week 5
- 8 Week 6
- 9 Week 7
- 10 Week 8
This is a summary/index table. Please follow the links in each cell for additional detail -- especially for the Deliverables column.
|Quizzes||10%||May be held during any class, usually at the start of class. A minimum of 5 one-page quizzes will be given. No make-up/retake option is offered if you miss a quiz. Lowest 3 scores will not be counted.|
|Labs||10%||See deliverables column above.|
|Project work||60%||November 21, December 10|
Friday (Sep 5)
Introduction to the Problem
- Most software is written in a high-level language which can be compiled into machine code for a specific architecture. However, there is a lot of existing code that contains some architecture-specific code fragments written in Assembly Language (or, in some cases, machine-specific high-level code).
- Reasons for writing code in Assembly Langauge include:
- Atomic Operations
- Direct access to hardware features, e.g., CPUID registers
- Most of the historical reasons for including assembler are no longer valid. Modern compilers can out-perform most hand-optimized assembly code, atomic operations can be handled by libraries or compiler intrinsics, and most hardware access should be performed through the operating system or appropriate libraries.
- A new architecture has appeared: Aarch64, which is part of ARMv8. This is the first new computer architecture to appear in several years (at least, the first mainstream computer architecture).
- There are over 1400 software packages/modules present in GNU Linux systems which contain architecture-specific assembly language code or have other portability issues. Most of these packages cannot be built on Aarch64 systems without modification.
In this course, you will:
- Select two software packages from a list compiled by Steve Macintyre of Linaro. Each of the packages on this list contains assembly language code which is platform-specific.
- Prepare a fix/patch for the software so that it will run on 64-bit ARM systems (aarch64). This may be done at either of two levels:
- Port - Add additional assembly language code for aarch64 (basic solution).
- Make Portable - Remove architecture-specific code, replacing it with compiler intrinsics or high-level code so that the software will successfully build on multiple platforms.
- Benchmark - Prove that your changes do not cause a performance regression on existing platforms, and that (ideally) it improves performance.
- Upstream your Code - Submitting your code to the upstream (originating) software project so that it can be incorporated into future versions of the software. This will involve going through a code review to ensure that your code is compatible with and acceptable to the upstream community.
General Course Information
- Course resources are linked from the CDOT wiki, starting at http://zenit.senecac.on.ca/wiki/index.php/SPO600 (Quick find: This page will usually be Google's top result for a search on "SPO600").
- Coursework is submitted by blogging.
- Quizzes will be short (1 page) and will be held without announcement at any time. Your lowest three quiz scores will not be counted, so do not worry if you miss one or two.
- Course marks (see Weekly Schedule for dates):
- 60% - Project Deliverables
- 20% - Communication (Blog and Wiki writing)
- 20% - Labs and Quizzes (10% labs - completed/not completed; 10% for quizzes - lowest 3 scores not counted)
- All classes will be held in an Active Learning Classroom -- you are encouraged to bring your own laptop to class. If you do not have a laptop, consider signing one out of the Learning Commons for class, or using a smartphone with an HDMI adapter.
- For more course information, refer to the SPO600 Weekly Schedule (this page), the Course Outline, and SPO600 Course Policies.
Discussion of how open source communities work
(Background for the Code Review Lab (Lab 1) which is homework due Week 2).
Week 1 Deliverables
- Set up your SPO600 Communication Tools - in particular, set up a blog and add it to Planet CDOT (via the Planet CDOT Feed List).
- Add yourself to the Fall 2014 SPO600 Participants page (leave the projects columns blank).
- Generate a pair of keys for SSH and email the public key to your professor.
- Sign and return the Open Source Professional Option Student Agreement.
- Set up a Fedora 20 system.
Tuesday (Sep 9)
Friday (Sep 12)
- Perform the Compiled C Lab (Lab 2) in groups
Week 2 Deliverables
- Complete and blog your conclusion to the Code Review Lab (Lab 1).
- Blog your conclusion to the Compiled C Lab (Lab 2)
This week your professor is at Linaro Connect, an engineering conference run by Linaro - a distributed not-for-profit collaborative technology company focused on Linux on ARM. You can participate remotely and may find some of the sessions interesting.
- Select and prepare to teach the class about a specific small topic related to assembly language / machine language programming.
Week 3 Deliverables
- Be prepared to give your presentation on Tuesday of next week (September 23).
Tuesday (Sep 23)
- Give your presentation about an assembly language topic - teach your SPO600 colleagues
Friday (Sep 26)
- Remainder of the presentations about an assembly language topic
- Introduction to assembly language
- Writing x86_64 and aarch64 code in the Assembly language lab (Lab 3)
Week 4 Deliverables
- Blog your presentation
Tuesday (Sep 30)
Friday (Oct 3)
The Linaro Performance Challenge is a project initiated by Jon "Maddog" Hall and Linaro to port or make portable open source software packages which contain platform-specific code and which may not build on the new Aarch64 architecture.
(There are two videos about the challenge, both of which are from late 2013 while the program was being finalized: One of an interview with Maddog and Steve Macintyre, and the other of a Linaro Connect presentation by Maddog).
The list of packages for this project was originally developed by the UK Debian developer Steve Macintyre, who works for Linaro. His focus in developing that list was to find packages that contained assembly language code for x86 (or other platforms) and which did not have assembly language code for ARM, especially Aarch64. As a result, the list includes many false-positives: there are many packages on there that can successfully build on ARM, either due to C work-arounds for the missing assembly code, or conditional compilation of the assembly code, or recent updates to the software, or other reasons.
In this class, we're going to start to triage this list by analyzing which packages exist in the Fedora package set and which have been successfully built for the aarch64 architecture.
The list has been processed with these steps:
- Grab the list of packages from the Linaro Performance Challenge site.
- Find out the corresponding names of the packages in the Fedora package set. Most of these will be the same as in the list, but some may be different.
- Find out which packages have not been built for Fedora on aarch64
- Divide the resulting list up between the members of the class for further analysis
Please see the Fall 2014 SPO600 Packages by Participant and perform the steps listed there.
Week 5 Deliverables
- Blog about the assembler lab (Lab 3).
- Do the tasks assigned on the Fall 2014 SPO600 Packages by Participant page, and blog about it.
Tuesday (Oct 7)
Jon "Maddog" Hall will be joining us for a remote talk and Q&A via Google Hangout.
Friday (Oct 10)
In groups, we'll be analyzing software pacakges from the Packages by Participant list to find the platform-specific code and build instructions.
Week 6 Deliverables
- Pick three additional packages (not the ones done in class) from your section of the Packages by Participant list and find the platform-specific code (or build instructions). Figure out what that code does, and document that on the list page. Blog about your results and your reflections on the task.
Tuesday (Oct 14)
Discussion of some of the reasons that platform specific (usually assembly language) code is used in software
Memory Barriers ensure that memory accesses are sequenced so that multiple threads, processes, cores, or IO devices see a predictable view of memory.
- Leif Lindholm provides an excellent explanation of memory barriers.
- Blog series - I recommend this series, especially the introduction, as a very clear explanation of memory barrier issues.
- Presentation at Embedded Linux Conference 2010 (Note: Acquire/Release in C++11 and ARMv8 aarch64 appeared after this presentation):
- Memory Barriers - A Hardware View for Software Hackers - This is a highly-rated paper that explains memory barrier issues - as the title suggests, it is designed to describe the hardware origin of the problem to software developers. Despite the fact that it is an introduction to the topic, it is still very technical.
- ARM Technical Support Knowlege Article - In what situations might I need to insert memory barrier instructions? - Note that there are some additional mechanisms present in ARMv8 aarch64, including Acquire/Release.
- Kernel Documentation on Memory Barriers - discusses the memory barrier issue generally, and the solutions used within the Linux kernel. This is part of the kernel documentation.
- Acquire-Release mechanisms
Atomics are operations which must be completed in a single step (or appear to be completed in a single step) without potential interruption.
- Wikipedia has a good basic overview of the need for atomicity in the article on Linerarizability
Friday (Oct 17)
- Compiler Intrinsics
- The use of compiler intrinsics (e.g., those in gcc, or in another compiler) locks you into the use of that specific compiler (or another that supports the exact same intrinsics), but it provides platform portability. It is better to use language features (e.g., C11 or C++11 atomic and acquire/release syntax) where possible, but since that is often not possible, the use of compiler intrinsics is more maintainable than inline assembly.
- GCC provides intrinsics (built-in functions) for atomic operations, as documented in the GCC manual:
- The Fedora project has some guidelines/recommendations for the use of these GCC builtins:
- Select your project(s):
- Fit between your skills and project needs
- Upstream status (e.g., dead project)
Week 7 Deliverables
- Select at least two software packages from the Linaro performance web site and/or the Packages page.
- Record your choice on:
- The Participants page - so that your colleagues in class know that you're working on the package(s). Note: Package choices will be approved by your professor, but will usually be accepted on a first-come, first-served basis.
- The Linaro performance web site - this will tell other people outside of our group within the Linux-on-ARM community that you are working on the package(s).
- Investigate and blog about your choice.
Over reading week:
- Contact the upstream communities for the packages you have selected -- so that they know that you are working on the package and to open a channel of communication for your forthcoming patches (or benchmarks, or other results).
- Formulate a work plan that will conclude with landing your software changes in the upstream software before the end of the course.
- Blog about your work plan and what you need to investigate/learn in order to complete your project.
Tuesday (Oct 28)
Working with the Code
- Working with GIT
- Working with other version control systems
Looking at How Distributions Package the Code
- Using fedpkg
Friday (Oct 31)
Week 8 Deliverables
- Blog about your progress connecting with the communities associated with your projects and working with the code.