[Pixman] [PATCH 07/15] pixman-filter: Speed up the BOX+BOX filter

[Oded Gabbay]

On Sat, Dec 12, 2015 at 8:06 PM,  <spitzak at gmail.com> wrote:
> From: Bill Spitzak <spitzak at gmail.com>
>
> This is easy as the caller already intersected the two boxes, so
> the width is the integral.
> ---
>  pixman/pixman-filter.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
> index 4aafa51..782f73d 100644
> --- a/pixman/pixman-filter.c
> +++ b/pixman/pixman-filter.c
> @@ -182,6 +182,11 @@ integral (pixman_kernel_t reconstruct, double x1,
>         assert (width == 0.0);
>         return filters[sample].func (x2 / scale);
>      }
> +    else if (reconstruct == PIXMAN_KERNEL_BOX && sample == PIXMAN_KERNEL_BOX)
> +    {
> +       assert (width <= 1.0);
> +       return width;
> +    }
>      else if (sample == PIXMAN_KERNEL_IMPULSE)
>      {
>         assert (width == 0.0);
> --
> 1.9.1
>
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As Soren said in his original email, this specialized case is
justified if we can demonstrate an improvement in a real-world
use-case, while making sure there aren't any other regressions.

Generally speaking, when adding specific conditions to optimize code
we need to see evidence that indeed the new code is faster in *most*
cases. This is because even if the added conditions improve
performance of a specific use-case, it might actually degrade
performance on most other cases as they now need to do additional
comparisons in every pass of this code.

Therefore, I think we need to see some real numbers to accept this patch.

fyi, I did a cairo benchmark run (on the trimmed benchmarks), and it
was practically unchanged. When I checked the results with
"--min-change 1%", I got:

Speedups
========
image  t-firefox-canvas-swscroll  691.34 (701.92 1.30%) -> 678.93
(693.67 1.25%):  1.02x speedup

image         t-firefox-fishtank  1611.65 (1640.22 1.23%) -> 1591.66
(1653.68 1.91%):  1.01x speedup

Slowdowns
=========
image     t-gnome-system-monitor  886.06 (893.33 1.20%) -> 895.76
(903.89 1.32%):  1.01x slowdown

image         t-firefox-fishbowl  3242.06 (3280.91 0.55%) -> 3284.20
(3285.17 0.08%):  1.01x slowdown

image                t-evolution  335.63 (337.11 0.28%) -> 340.48
(352.97 1.62%):  1.01x slowdown

image        t-xfce4-terminal-a1  554.95 (572.35 1.59%) -> 563.67
(582.91 1.62%):  1.02x slowdown

image       t-gnome-terminal-vim  354.85 (358.67 0.67%) -> 364.49
(366.12 0.33%):  1.03x slowdown

      Oded