VNC console page gets too slow when with Google Chrome

Bug #1653686 reported by sean redmond
This bug affects 3 people
Affects Status Importance Assigned to Milestone
novnc (Ubuntu)

Bug Description

See bug reported in the wrong location here

This seems to be fixed in novnc 0.6.1 ( But I could not find an ubuntu .deb for this version.

Also see Red Hat bug report here

Tags: patch
Revision history for this message
Launchpad Janitor (janitor) wrote :

Status changed to 'Confirmed' because the bug affects multiple users.

Changed in novnc (Ubuntu):
status: New → Confirmed
Revision history for this message
Michael Eischer (eischer) wrote :

The performance problems also affects Firefox (current and past versions) but not as bad as Chrome. The issue is caused by a very inefficient handling of the zlib decompression window. Upstream fixed the problem by replacing the zlib library with an efficient one.

In case updating the novnc version on Trusty or Xenial is no option, I've implemented a workaround for the performance issue on Trusty.

vnc-perffix.patch works around the performance issue by shortening the decompression window to its expected size only once it is four times bigger than expected. Which isn't too bad from a memory consumption point of view as the expected windows size is only 32k byte entries. Without the patch the zlib window is shortened after a few bytes have been added, causing a full copy just to remove a few bytes. I've also replaced to call to Array.slice with a simple loop for copying as it speedup the window copy by an order of magnitude in Chrome. (Seems like the code managed to confuse the JIT).

Revision history for this message
Michael Eischer (eischer) wrote :

vnc-jsunzip-ring.js.patch is a proper fix uses the decompression window as a ring buffer thus avoiding any problems with limiting the window size.

Revision history for this message
Ubuntu Foundations Team Bug Bot (crichton) wrote :

The attachment "vnc-perffix.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

tags: added: patch
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