[Regression 1.12->1.13] "read from connection when polling" causes video to freeze

Submitted by John Lindgren

Assigned to xcb mailing list dummy

Link to original bug (#106405)

Description

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: commit fad81b63

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