Bug 493730

Created attachment 337920 [details]
sysprof save of slowness

Description of problem:
I've been testing the latest rawhide on my x1950pro with kms + composting the last few days. Using a standard gnome desktops with 3d effects enabled.

And I've noticed that sometimes X freezes for upto 2 seconds, the mouse pointer still moves, but doesn't change when it should, clicking on / in non of the windows works, clicks do get registered when it unfreezes.

The easiest way to reproduce is to open 2 (or more tabs) in firefox and
switch between them, for example these 2 work for me to reproduce:
http://koji.fedoraproject.org/koji/buildinfo?buildID=93907
http://koji.fedoraproject.org/koji/buildinfo?buildID=95894

Open these 2 and then switching between the 2 tabs, (or away / from firefox),
causes the freezes. Note that the freeze does not always happen, but only sometimes (circa 50% of the time).

This is similar in many ways to bug 469378, yet very different, as it does not always happen (where as 469378 did have 100% reproducability).

Also interesting is that when switching tabs, the webpage gets successfully
rendered, and one can even enter for example 1 or 2 chars in a textinput field,
and then X freezes.

I've done some sysprof-ing of the stalls and this clearly points to a software
fall back happening. But why only sometimes? I guess that some special memory
allocation operation (GEM / TTM memory) fails and then a software fallback is used to work around this.

I can compile the driver with software fallback debugging turned on and get an Xorg.log with that in if you want (what was the define again and in which file does it live?).