ubuntu-x-swat team mailing list archive

[Sitsofe Wheeler <745608@xxxxxxxxxxxxxxxxxx>]

Ferry:
I actually don't know why it works :) Sadly I didn't get to that option by logical deduction but rather by trying everything I could... My guess is that there is a race happening where a buffer is being reused while it actually still in use. Here's what the intel man page says about the DebugWait option:

Option "DebugWait" "boolean"
Wait for the completion of every batch buffer before continuing, i.e. perform synchronous rendering.
Default: Disabled

So this changes from submitting batch buffers and *not* waiting for a
reply to waiting for a reply after submitting each batch buffer (so
effectively you can no longer simultaneously submit multiple batch
buffers). This should also hurt speed as it is no longer possible to do
so much at once so it's strange you are seeing a speed improvement...

There is also some slight evidence that this is a locking issue. Over on
https://bugs.freedesktop.org/show_bug.cgi?id=36326#c8 I tried to find
why certain old kernels don't show the issue and that narrowed down it
down to a patch that removed the Big Kernel Lock (BKL) from various
functions of the i915 driver presumably allowing more overlap.

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https://bugs.launchpad.net/bugs/745608

Title:
  [915GM] font corruption on Intel GMA900