GIT Rebase in contributing opensource.

Simply introduce GIT Rebase command comparing GIT Merge

If you've been contributing linux-perf ..
1. origin = my remote repository
2. upstream = linux-perf remote repository
3. origin/master = to follow one branch of 'upstream'

If you’ve been working in ‘origin/master’ but ‘upstream’ is updated so you need to update your remote and local repository.
If you do..
After you make yours newest, you can do as below.
(ex> ‘git fetch upstream perf/core’ )

1) git rebase

$ git fetch upstream perf/core
$ git rebase upstream/perf/core (on 'master' branch)
# Contents of your commit is added on top of the newest commit history.