Bug 78713

Summary:

Vertical sync (vsync) broken on Radeon HD 4670

Product:

xorg

Reporter:

James Le Cuirot <chewi>

Component:

Driver/Radeon

Assignee:

xf86-video-ati maintainers <xorg-driver-ati>

Status:

RESOLVED INVALID

QA Contact:

Xorg Project Team <xorg-team>

Severity:

normal

Priority:

medium

Version:

git

Hardware:

x86-64 (AMD64)

OS:

Linux (All)

Whiteboard:

i915 platform:

i915 features:

Attachments:

Description	Flags
Xorg.0.log	none

Description James Le Cuirot 2014-05-14 23:04:53 UTC

I know that vsync worked on Radeon Zaphod mode when bug #29726 was fixed but it has broken at some point since. I am now observing tearing in glxgears even when it reports that vsync is enabled. Unfortunately I have no idea exactly when it broke. The good news is I have a very strong clue as to what the problem is. If you remove this line...

http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/tree/src/radeon_dri2.c?id=be1469cc23aba46daf3293b3d09c5f2e792e7f42#n480

...then it works. Why? I wish I knew. It was just a very lucky stab in the dark. This line was around a good deal before bug #29726 was fixed so presumably its interaction with something else must have changed in the meantime. SwapbuffersWait is definitely enabled.

Comment 1 James Le Cuirot 2014-05-14 23:08:31 UTC

Created attachment 99049 [details]
Xorg.0.log

Comment 2 James Le Cuirot 2014-05-14 23:23:39 UTC

Hmmm. I was about to go to bed when it suddenly occurred to me that I hadn't tried it without Zaphod mode. I just kinda assumed it had something to do with that. It turns out not. I deleted my xorg.conf altogether and sure enough, I get the exact same behaviour with the tearing occurring unless I remove that line. For the record, I don't have a .drirc.

Comment 3 James Le Cuirot 2014-07-05 08:31:26 UTC

The problem persists in xf86-video-ati-7.4.0. The workaround still works.

Comment 4 Michel Dänzer 2014-07-09 03:25:08 UTC

Removing that line has basically the same effect as Option "EXAVSync". If you get tearing without that, you're probably using a compositing manager (which probably doesn't use OpenGL for rendering).

Comment 5 James Le Cuirot 2014-07-09 20:38:54 UTC

Hmm you're right. I'm using xfwm4 but only 4.10. I thought OpenGL had been standard fare for compositors for a while but that and vsync was only added in 4.11. I've now tried that but it only seems effective on the first display. There is Compton but I'll just pass on a compositor until I switch to Wayland. Thanks. :)

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