[Bug 55500] [sna gen4] corrupt rendering (and flickering on redraw)

[bugzilla-daemon at freedesktop.org]

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

--- Comment #97 from Zdenek Kabelac <zdenek.kabelac at gmail.com> ---
(In reply to comment #96)
> (In reply to comment #93)
> > The bad part is - while before I've been getting 3.7Mchar/s in x11perf
> > -aa10text - now it's like 1.3Mchar/s  so significantly slower.
> 
> That's the sacrifice, we have to stop sending commands to the GPU and wait
> for it complete those in flight (quite frequently). Or else new rectangles
> overwrite vertex entries still being used by later entries 
> 
> > So the question here would be - isn't the corruption based on  triangle
> > surface size ? So i.e. GPU is able to  process a lot of small ones - but has
> > bug with bigger ones ?
> > 

But as I said before - if that would be plain hw defect - IMHO it would simply
always appear - but it seems like it's working for a while - then 'something'
happens - and flickering starts to appear - with (assumingly) same amount
of texels/triangle/vertices - and than something again may happen,
and the problem is gone for a while.

> Not really, you have to predict when a VUE being used by the end of the
> pipeline will be overwritten by a new rectangle at the start of the
> pipeline. This is completely internal state - the primitive command we want
> to feed to the GPU can contains thousands of rectangles. Instead of counting

Well I've tried even 8 max triangles - and the error appeared after a while,
so far '6' is magic.

> rectangles, you want to start counting fragments (actually texel reads since
> that will be the ratelimiting factor) and flush if we queue up too much work
> for the GPU. If you also model how fast the gpu is retiring fragments so

But in case the same page is rendered with problems as well as without
problems,
then it doesn't look like texel read is problem, it rather looks like some
kind of memory mapping/ordering.

Also is there some explanation why  intel_gpu_top is showing so much higher GPU
usage when the flickering is visible ?

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