Triangle tearing (this is not exact definition of what you can see on attached screenshots, but the point is - this artifact seems like occur under similar conditions as typical tearing, and most of the time looks like triangle) is observer for example while fast scrolling or selecting text in Konsole or scrolling folder with many files in Dolphin, and so on. But, for some reason, not while video playback (xv, opengl and vaapi video outputs tested).
Reproducible in: Mesa 10.3.2 and driver version 2.99.914-1~exp1ubuntu4.1 with SNA acceleration, Mesa 10.5~git1501311930.609461 and driver version .99.917+git1501311931.dac01d with both of SNA and GLAMOR acceleration.
Not reproducible in: Mesa 10.3.2 and driver version 2.99.914-1~exp1ubuntu4.1 with GLAMOR acceleration.
(Actually, I not sure issue in driver, because I just compare default Kubuntu 14.10 packages set (libdrm, video driver, mesa, etc.) and set from Oibaf PPA, but since there is difference between SNA and GLAMOR I this is issue in the driver.)
Change kernel version seems like doesn't make any difference. For example with Mesa 10.3.2 and driver version 2.99.914-1~exp1ubuntu4.1 with GLAMOR acceleration there is no tearing on stock Linux 3.16.0-30 from repo and on Linux 3.18.5. Boot Linux 3.16.0-30 with Mesa 10.5~git1501311930.609461 and driver version 2.99.917+git1501311931.dac01d gave tearing anyway.
I tried TearFree with Mesa 10.5~git1501311930.609461 and driver version 2.99.917+git1501311931.dac01d with SNA, but TearFree doesn't help.
In SNA mode I tested kwin, and in GLAMOR mode I tested kwin_gles (4.11.12) in both cases in Full repaint V-Sync mode in KWin settings.
With disabled desktop effects I doesn't see this artifact (not reproducible or I just can't notice it).
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Hardware is the same as described in comment 10 in this bugreport: https://bugs.freedesktop.org/show_bug.cgi?id=47858#c10
What it looks like is the compositor is sampling the updated pixmaps in the middle of a cache flush. The triangle artifacts is symptomatic of how OpenGL renders, but the actual corruption looks to be at the individual EU/thread level i.e. sampling. Given that there is supposed to be a full cache flush between X rendering and the compositor (and vice versa), that is surprising!
Can you please try Option "AccelMethod" "blt"? Could you also find a really old version of mesa, say even 9.0 or 10.0? Could you try a few different kernels?
> Can you please try Option "AccelMethod" "blt"?
Just tested it, same result as with SNA on Mesa 10.3 and 10.5 and GLAMOR on Mesa 10.5.
> Could you also find a really old version of mesa, say even 9.0 or 10.0? Could you try a few different kernels?
I may try Kubuntu 12.10 (Linux 3.5, Mesa 9.0) Kubuntu 13.04 (Linux 3.8, Mesa 9.1.1) and Kubuntu 13.10 (Linux 3.11, Mesa 10.0) LiveCD's. That would be fine?
Or, if I need to test older kernels especially with Mesa 10.5, plese let me know which versions I need to download.
For testing, ideally we would only change one component at a time. However, if you have liveds with different configuration, that may help identify when it starts and indeed be useful.
Kubuntu 12.10: Linux 3.5.0, UXA, Mesa 9.0.0, KDE 4.9.2
Kubuntu 13.04: Linux 3.8.0, SNA, Mesa 9.1.1, KDE 4.10.2
Issue is reproducible in Kubuntu 13.04, but not reproducible in Kubuntu 12.10.
Hmm, I wonder if we can start from 12.10 and install components piecemeal until it fails. I doubt that is very practical.
What may be easier is to start with 13.04 and downgrade mesa to 9.0.0 by compiling it by hand, and similarly for the kernel. You can also flip the xf86-video-intel over to UXA (but given how it persists between UXA/SNA/blt/glamor on tip, I guess it is not the ddx).
I would start with compiling mesa.
I guess something like apt-get build-dep libgl1-mesa-dri and git clone git://anongit.freedesktop.org/mesa/mesa and a bare ./configure --prefix=/usr should be enough to achieve the downgrade. (If you want to be safer, just build a chroot for 13.04.)
I tried few different combinations as you suggested:
1. Kubuntu 12.10, Mesa 9.0.0, UXA, but kernel changed from 3.5.0 to 3.8.0 - issue still not reproducible, so I didn't tried to downgrade kernel on 13.04.
2. Kubuntu 13.04, Mesa 9.1.1, SNA - issue is reproducible.
3. Kubuntu 13.04, Mesa 9.1.1, UXA - issue is not reproducible.
4. Kubuntu 13.04, Mesa 9.0.0, SNA - issue is reproducible.
5. Kubuntu 13.04, Mesa 9.0.0, UXA - issue is not reproducible.
So, seems like issue wasn't reproducible with Kubuntu 12.10 just because UXA was default. If necessary, I could install Kubuntu 12.10 back and check if I will able to reproduce it with default software set (Linux 3.5.0, Mesa 9.0.0) but change AccelMethod to SNA.
I also notice exactly same artifact in text installer (mini.iso) of Ubuntu 15.04 (Linux 3.19) so I download text-mode installer of previous releases and find out that it's also reproducible with text installer of 14.04 (Linux 3.13) and 14.10 (Linux 3.16) installers, but not with 13.10 (Linux 3.11).
Please ignore part about text mode installers, because I noticed that this corruption in text mode installers is probably different issue - it also reproducible in KVM, so this is unrelated to Intel GPU's.