Created attachment 99352 [details]
dmesg output

Created attachment 99353 [details]
glxinfo output

LIBGL_DEBUG=verbose glxinfo outputs the following : 

libGL: screen 0 does not appear to be DRI3 capable
libGL: pci id for fd 4: 8086:0152, driver i965
libGL: OpenDriver: trying /usr/lib/x86_64-linux-gnu/dri/tls/i965_dri.so
libGL: OpenDriver: trying /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
libGL: Can't open configuration file /home/andrew/.drirc: No such file or directory.
libGL: Can't open configuration file /home/andrew/.drirc: No such file or directory.
libGL: Can't open configuration file /home/andrew/.drirc: No such file or directory.

Created attachment 99354 [details]
xorg log

First please update mesa to eliminate one known IVB display corruption bug.

Mesa updated to 10.3.0-devel from oibaf's PPA. No change. glxgears shows severe rendering artefacts. (see attachment)

Created attachment 99357 [details]
glxgears rendering artifacts

How about going the other way, and looking for a version of packages that used to work? Then find which package seems to cause the regression. The choice is kernel / ddx / mesa. So far we know that mesa has a few issues, but they may be unrelated.

Added the following to xorg.conf

Option "AccelMethod" "uxa"

This has removed the speckling artifacts. I am still having issues with glxgears not rendering correctly, but this is definitely an improvement.

Sadly, that still doesn't rule out a root cause in mesa.

I've tried the latest Mesa Release Candidate (10.2 rc3) and 9.2.5 - no change. As I said, changing the acceleration mode fixes the speckling artifacts but OpenGL applications have severe vertical tearing artifacts when rendering in hardware.

Unsure where to go from here - I haven't seen anyone else report the problem so is this likely a hardware issue? Windows drivers exhibit no problems but I'm not sure if that means anything.

Cheers,
Andrew.

The speckle looks to be a blend failure. It looks to be in the compositor as the pattern seems to have some of the overdrawn content, which is why I suspect that mesa is involved. At first I thought the speckle would be a cache invalidate issue, but it doesn't actually seem to be wide enough for a cacheline issue - so it may be a bad EU, sampler or killpixel instruction.

When you tried 9.2.6, what changed? Presumably the glxgears returned to normal?

9.2.5 still rendered with artifacts. I tried with 9.0.3 and it renders fine. Would it be helpful if I find the exact version where it breaks?

Cheers,
Andrew.

Ok, it definitely broke between 9.0.3 and 9.1, and seen as that's when OpenGL 3 support was introduced I suspect that's probably important.

Let me know if there's anything else I can do.

Cheers,
Andrew.

I've lost track. Are you referring to the speckle or the glxgears corruption that disappears with 9.0?

Ok it looks like the two issues are distinct.

 - Speckling disappears by changing the kernel module's acceleration method to UXA, but is unaffected by any of the Mesa version changes

 - GL rendering artifacts clear up on reverting to Mesa 9.0.3 ( and reappear after 9.1 ) but are unaffected by the kernel module's acceleration method.

Time to do a new round of testing: kernel for any w/a, ddx and mesa for any fixes.

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