[Xcb] [Bug 106405] New: [Regression 1.12->1.13] "read from connection when polling" causes video to freeze

[b***@freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106405

Bug ID: 106405
Summary: [Regression 1.12->1.13] "read from connection when
polling" causes video to freeze
Product: XCB
Version: unspecified
Hardware: x86-64 (AMD64)
OS: Linux (All)
Status: NEW
Severity: normal
Priority: medium
Component: Library
Assignee: ***@lists.freedesktop.org
Reporter: ***@jlindgren.net
QA Contact: ***@lists.freedesktop.org

After updating libxcb to 1.13, video intermittently freezes in Skype calls.
Actually, it's not just the video stream that hangs, the whole Skype window
freezes temporarily (1-10 seconds). Switching in/out of fullscreen gets things
moving again.

The hangs are most noticeable in Skype (which is Chromium-based) but also occur
occasionally in Chromium itself; I have seen brief but definite
freezes/stutters in YouTube and Netflix video, as well as scrolling through at
least some web pages (amazon.com for example).

Reverting the following commit makes everything smooth again:
https://cgit.freedesktop.org/xcb/libxcb/commit/?id=fad81b63422105f9345215ab2716c4b804ec7986

Since Skype and Chromium share the same codebase, and I haven't seen freezes in
other applications, it could be a bug in Chromium that is merely triggered by
the libxcb change. I don't know enough of the internals of either project to
say which is at fault.

Disabling compositing (compton) seemed to work around the issue but of course
leads video tearing, which is no less annoying.

Arch Linux x86_64 w/ kernel 4.16.5-1
Intel (Skylake) graphics w/ modesetting driver + DRI2
Xorg 1.19.6+13+gd0d1a694f-2
Mesa 18.0.1-1
Compton 0.1_beta2.5-10 w/ GLX backend