Possible problems with Intel drivers in 4.5.0 release
kde at martin-graesslin.com
Mon Aug 2 20:59:24 CEST 2010
I know that the release is scheduled for tomorrow, nevertheless I want to make
you aware of a possible problem with Intel graphics cards and compositing.
I think I first have to explain a little bit: KWin uses a test to determine if
OpenGL compositing is working during the startup. This seems to fail for some
Intel drivers since some time. It used to work and the code has not changed,
so it is most likely a driver bug. I was first made aware of this problem at
Akademy. Due to the fact that I do not own Intel hardware I was unable to
reproduce or try to fix the issue.
Up to 4.4 KWin just disabled compositing if this check during startup failed.
In the 4.5 development cycle it was changed to fall back to XRender
compositing. The idea behind it was that you get translucancy when starting
from live cd or running in a virtual machine. It was not meant for the case
that the OpenGL driver causes an incorrect self check failure.
This fallback to XRender causes slowness of the system and some effects not
working. Furthermore the complete UI says that it is using OpenGL compositing
although in truth XRender is used.
When I was made aware of this problem with Intel drivers I reverted the
fallback to XRender both in trunk and branch (svn revs 1148315 and 1148316).
Unfortunately I missed one change (the original commit changed more than just
the fallback) which I found by pure luck this weekend (svn commit 1157978).
It's confirmed that this commit is now finally working: compositing is
disabled at startup. By disabling the functionality checks in the advanced
compositing preferences it is possible to get OpenGL compositing working
Now the question is what to do with this commit. Due to the fact that I missed
this one line KWin is now saying that it disables compositing but in truth is
falling back to XRender. I see three possible solutions:
1. We ignore it. This might result in many complaints about slow KWin and that
effects are not working any more (e.g. cube, coverswitch, blur, etc.). We will
have many complaints about slow KWin anyway due to the enabling of blur and
the fact that many drivers are too bad for it. On the other hand we had no bug
report to this issue. I only heard about this problem by fellow KDE
developers, which might be related to the fact that we have more recent
drivers/Xorg than most of our users.
2. We backport this patch to 4.5.0. This means a lot of work due to the
schedule (sorry for writing that late, I had to think about this issue for one
day) and will cause users not be able to use desktop effects any more. But it
would be the cleanest one.
3. We backport to 4.5.1. This would mean a behavior change between 4.5.0 and
4.5.1 which I would not like.
To summarize: I am not happy with any of the three options I came up with. And
I do not know what to do about it. Given that the release is tomorrow I guess
it's only possible to choose between option 1 and 3, while I think option 2
would be the best. I think it's better to disable compositing instead of slow
compositing. So the question is, if we should backport the commit for 4.5.1.
The best solution would be to fix the failing self check. But due to missing
hardware I am not able to investigate it.
Sorry for writing that late
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