Last Class

• Flynn's taxonomy (SISD, SIMD, MIMD, MISD)
• Shared memory vs Distributed memory (and Hybrid model)
• Amdahl's law (speedup < 1/(s + (1-s)/p))
• Load balancing (static vs dynamic)
• Scalability (strong and weak)
• Reasons for poor scalability (Amdahl's law, load imbalance)
• Shared memory model (OpenMP, POSIX, PGAS)
  • process vs thread
  • Symmetric multiprocessing vs CC-NUMA
  • Race conditions: multiple threads accessing the same memory location when at least one thread is writing
• OpenMP
  • fork-join model
  • pragmas (#pragma omp <parallel, for, sections, section, master, single, critical, berrier>)
  • additional options: schedule(static/dynamic/guided/runtime), reduction(+:sum), nowait
  • functions (#include <omp.h>, omp_get_max_threads(), omp_get_num_threads(), omp_get_thread_num(), omp_set_num_threads())
  • environment variables (OMP_NUM_THREADS, )
• Git: config, clone, add, commit, pull, push

This Class

• Advanced OpenMP
  • False sharing (cacheline)
  • CC-NUMA (sockets, cores, NUMA-nodes, first-touch)
  • Nested parallelism, parallel for collapse(2)
  • Memory models (weak sequential consistency)
  • Synchronization: atomic, flush, locks (omp_lock_t)
  • Thread affinity: OMP_PLACES=(cores/socket), OMP_PROC_BIND=(close/spread), OMP_DISPLAY_ENV=true)
• Git: merging
• Makefile: variables, rules, targets, dependency list, make -j

Git

Basic commands

git init                         # initialize a directory as a new repository
git add <file-name>              # add new file or changes to an existing file to be commited (also called staging)
git commit -m '<commit-message>' # commit staged changes
git pull                         # pull changes from the remote repository
git push                         # push changes to a remote repository

git clone <repo-path>            # clone a repository

git status                       # show current status of the repository
git diff                         # show unstaged changes in the repository
git diff --cached                # show staged changes in the repository
git diff <file-name>             # show changes to a particular file

Mergin (two ways)

Stash, pull and commit

git add <files>
git stash
git pull
git stash pop
# resolve any merge conflicts
git stash clear
git add <files>
git commit 'merged'

Commit, pull and commit

git add <files>
git commit -m 'message'
git pull
# resolve any merge conflicts
git add <files>
git commit

git log

> git log

commit 2b3ba91d4ad98c33aade864c46a705e96f6c2985
Author: Dhairya Malhotra <dmalhotra@ices.utexas.edu>
Date:   Thu Jan 19 15:46:39 2017 -0600

    Add .gitignore

commit 7b81413e6bec668af4b4aa52a8774784c778e2c8
Author: Dhairya Malhotra <dmalhotra@ices.utexas.edu>
Date:   Thu Jan 19 15:41:19 2017 -0600

    Minor changes

commit bb89504a2cb24767ad68b1ae611baa8e2da0865f
Author: Dhairya Malhotra <dmalhotra@ices.utexas.edu>
Date:   Thu Jan 19 15:07:05 2017 -0600

    Initial commit

alias gg='git log --oneline --abbrev-commit --all --graph --decorate --color'

> gg
*   4481a65 (HEAD, master) merged
|\
| * 7fa895c (origin/master, origin/HEAD) more text
* | 3264c75 some more
|/
* 5ecb7e0 add text
* f6f082b add readme

GUI view

gitk [options]