[Mesa-dev] [PATCH 0/7] vbo: introduce a minmax_index cache

[Timothy Arceri]

On Thu, 2016-01-07 at 19:57 -0500, Nicolai Hähnle wrote:
> Hi,
> 
> this series is intended to address a (big) part of the performance
> problems
> that occur when games use an index buffer from a VBO together with
> vertex
> attributes supplied by user pointer. On a lower-end Radeon (Carrizo),
> it
> lifts This War Of Mine (the worst offender I've seen) from basically
> unplayable
> to an acceptable ~22fps.

Hi Nicolai,

A while back I added a SSE41 min/max optimisation for the INT path. I
never added it to BYTE/SHORT as the games I was benchmarking never hit
those paths. It would be interesting to know which path "This War Of
Mine" is hitting.

A quick Google shows Carrizo should have SSE41 right?



> 
> There are really two parts to the performance inefficiency:
> (1) the fact that we have to compute min/max in the first place
> (2) the fact that games developers like to helpfully declare the
> index buffer
> as STATIC_DRAW, which means it ends up in VRAM, making things much
> worse than
> they would be with (1) alone.
> 
> The series does this simply by caching (or memoizing, if you like)
> the result
> of vbo_get_minmax_indices. This makes sense since while the caching
> itself of
> course has some overhead, it is only used for VBOs - and the people
> who mix
> VBO index buffers with non-VBO vertex data seem to do so precisely
> because
> their index buffers are static, hence caching is a win.
> 
> The cache is disabled permanently for VBOs that we detect to be
> written to by
> GPU operations. It is invalidated on other writes (Buffer(Sub)Data
> etc.).
> 
> I originally considered putting the caching in st/mesa instead of
> vbo, but that
> would have required duplicating some of the logic in
> vbo_get_minmax_indices for
> iterating over primitives inside the Gallium statetracker. I wanted
> to avoid
> this code duplication, hence why I put it in vbo.
> 
> Please review!
> 
> Thanks,
> Nicolai
> --
>  src/mesa/Makefile.sources             |   1 +
>  src/mesa/main/bufferobj.c             |  41 +++-
>  src/mesa/main/mtypes.h                |   7 +
>  src/mesa/main/transformfeedback.h     |   3 +
>  src/mesa/vbo/vbo.h                    |   3 +
>  src/mesa/vbo/vbo_exec_array.c         | 148 ------------
>  src/mesa/vbo/vbo_minmax_index.c       | 342
> ++++++++++++++++++++++++++++
>  src/util/hash_table.c                 |  25 ++
>  src/util/hash_table.h                 |   2 +
>  src/util/tests/hash_table/Makefile.am |   1 +
>  src/util/tests/hash_table/clear.c     |  91 ++++++++
>  11 files changed, 507 insertions(+), 157 deletions(-)
> 
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