The trace-viewer directory contains code from: http://trace-viewer.googlecode.com/svn/trunk/ The file UPSTREAM_REVISION contains the upstream revision number that was last pulled. Changes should be made upstream and then pulled into the trace-viewer directory. The update.py script should be used to pull the latest upstream code, update the UPSTREAM_REVISION file, and package the CSS and Javascript files into style.css and script.js, respectively. These generated files are being checked into the git repository, and they get embedded in each trace HTML file that systrace.py generates. To make development of trace-viewer code in the context of systrace easier, systrace supports arguments to generate HTML files that link to files in a trace-viewer development directory rather than embedding the JS and CSS in the HTML. Do take advantage of this, you should check out the trace-viewer code in a new directory (e.g. trace-viewer-dev) and use systrace as follows: $ ./systrace.py --link-assets --asset-dir trace-viewer-dev