[Bug 55500] [sna gen4] corrupt rendering (including wrong rendering of characters and flickering on redraw)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=55500

--- Comment #137 from Zdenek Kabelac <zdenek.kabelac at gmail.com> ---
(In reply to comment #136)
> The issue that the VUE (which is a memory slot used by the GPU for a vertex
> entry) are reused by a second thread before the first thread is complete,
> causing the first thread to generate invalid texture coordinates and corrupt
> rendering. That is a hardware read-write hazard bug (or at least I have not
> found any controls in the EU state to prevent it).

I don't think it's that easy to explain -

The typical problem in my case is -  when I freshly start the Xsession -
I do not observe any rendering bug.  I need to use this machine for a while,
to start to get those errors.

So if there would be some 'easy to trigger hardware race' - it should be
reproducible all the time.

But in my case it seem - the probability increases over the time heavily -
maybe with the amount of  cached BO segments ?

Or maybe it depends on how the memory order is set - i.e. the problem is
triggered when certain memory read pattern start to appear ?

Since once the issue of flicker starts - it then happens all the time - and
then suddenly it disappears for a while again ?

So maybe there needs to be prohibited some memory offset/alignment of buffers
with vertices ?

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