[Mesa-dev] [RFC PATCH 1/2] r600/sb: Set flags for GROUP_BARRIER instruction and force it into slot X

[Gert Wollny]

Am Donnerstag, den 11.01.2018, 08:09 +0100 schrieb Gert Wollny:
> Am Mittwoch, den 10.01.2018, 15:27 -0500 schrieb Ilia Mirkin:
> [...]
> > 
> > If your hardware executes all the vertices in parallel, then a
> > barrier should be unnecessary.
> 
> My first try for this patch did not include forcing the barrier into
> slot x, which in turn resulted in failing piglits, e.g.
> 
>    tcs-output-array-float-index-rd-after-barrier
> 
> and I'm quite confident that the LDS r/w order was not broken - also
> because just forcing the barrier into slot x fixed it, so I guess not
> all vertices are always processed in parallel, which is also no
> surprise since the number of shader units attributed to the TCS stage
> is limited.
Dropping the barrier altogether doesn't have an impact on the
tesselation/barrier piglits, but I still wonder what happens if there
are more vertices to be processed than there are shader units so that
they can not be processes in parallel ...