Graph processing is slow, freezes tabs

[psybuzz]

The Graph v1 dashboard currently builds the layout for its graph on the main thread. While the graph is loading (progress bar shows reading pbtxt, parsing, etc) the user can switch to another dashboard and see an unresponsive UI. For example, switching to the Scalars dashboard while the Graph is loading, and being unable to click on anything.

This performance recently regressed from Chromium M79 to M80. In M79, a case that used to freeze the tab for ~4 sec now freezes the TensorBoard for ~50sec, rendering it unusable.

Sample performance trace:

We should invest in either

• Moving heavy JS work from the main thread to a worker
• Producing a small reproducible case and filing a bug against Chromium to fix the performance regression

[mherzog01]

Not sure if it's related, but the following is a simple way to cause large performance problems in TensorBoard graph displays: https://stackoverflow.com/questions/63893714/tensorboard-hangs-when-visualizing-an-object-detection-graph.