[Mesa-dev] Possible ideas for optimisations in Mesa

[Marek Olšák]

On Fri, Apr 17, 2015 at 1:21 PM, Timothy Arceri <t_arceri at yahoo.com.au> wrote:
> Hi all,
>
> Last year I spent a whole bunch of time profiling Mesa looking for areas
> where improvements could be made. Anyway I thought I'd point out a
> couple of things, and see if anyone thinks these are worthwhile
> following up.
>
> 1. While the hash table has been getting a lot of attention lately,
> after running the TF2 benchmark one place that showed up as using more
> cpu  than the hash table was the glsl parser. I guess this can be mostly
> solved once mesa has a disk cache for shaders.
>
> But something I came across at the time was this paper describing
> modifying (with apparently little effort) bison to generate a hardcoded
> parser that 2.5-6.5 times faster will generating a slightly bigger
> binary [1].
>
> The resulting project has been lost in the sands of time unfortunately
> so I couldn't try it out.
>
> 2. On most of the old quake engine benchmarks the Intel driver spends
> between 3-4.5% of its time or 400 million calls to glib since this code
> can't be inlined in this bit of code from copy_array_to_vbo_array():
>
>       while (count--) {
>          memcpy(dst, src, dst_stride);
>          src += src_stride;
>          dst += dst_stride;
>       }
>
> I looked in other drivers but I couldn't see them doing this kind of
> thing. I'd imaging because of its nature this code could be a bottle
> neck. Is there any easy ways to avoid doing this type of copy? Or would
> the only thing possible be to write a complex optimisation?

Yeah, other drivers don't do this. In Gallium, we don't change the
stride when uploading buffers, so in our case src_stride ==
dst_stride.

Marek