[Mesa-dev] [PATCH 0/4] GLSL passes begone

[Matt Turner]

On Thu, Apr 6, 2017 at 12:49 PM, Thomas Helland
<thomashelland90 at gmail.com> wrote:
> This series has been reciding on my computer for way to long,
> so it's about time I get it out there for some feedback.
> The rationale is that in the glsl compiler a lot of the overhead
> is in cache misses due to the visitor pattern we're running.

perf can measure various kinds of cache misses. It would be good to
confirm your hypothesis.

> This is run on my intel machine.
>
> Here are some perf stat results before and after the series
> on a shader-db run on a subset of my shader-db.
>
> Before:
> 56 849 919 924    cycles:u                  #    2,894 GHz
> 21 803 529 990    stalled-cycles-frontend:u #   38,35% frontend cycles idle
> 82 463 039 717    instructions:u            #    1,45 insn per cycle
>                                             #    0,26  stalled cycles per insn
> 16 796 501 647    branches:u                #  855,182 M/sec
>    394 313 169    branch-misses:u           #    2,35% of all branches
>
> 20,568256999 seconds time elapsed
>
>
> After:
> 55 956 131 481    cycles:u                  #    2,884 GHz
> 21 889 872 343    stalled-cycles-frontend:u #   39,12% frontend cycles idle
> 80 666 584 607    instructions:u            #    1,44  insn per cycle
>                                             #    0,27  stalled cycles per insn
> 16 349 063 938    branches:u                #  842,630 M/sec
>    383 226 870    branch-misses:u           #    2,34% of all branches
>
> 20,342067729 seconds time elapsed
>
> So, some things to notice:
> There's a decent drop in executed instructions.
> There's an increase in stalled cycles, which is not what I expected.
> We are still seeing an ever so slight reduction in runtime.
> Fewer branches, and fewer branch-prediction misses.
>
> The question is if this is a route we want to go down?

I think so!

>From a quick glance the series looks nice. I'll review in more depth soon.