Some notes on optimization work in progress (was: Re: [cairo] WinXp benchmarks)

[Soeren Sandmann]

Carl Worth <cworth at redhat.com> writes:

> Here's an update on where that work stands. First, I've chosen
> gearflowers.svg[*] as a profile image. It's a rather complex image
> with lots of splines, a mixture of strokes and fills, and a *lot* of
> gradients.
> 
> Rendering this image with current cairo takes about 5-7 seconds on my
> laptop. Here's how that breaks down under oprofile (using a slightly
> modified version of svg2png that produces no output PNG file):
> 
> 	CPU: CPU with timer interrupt, speed 0 MHz (estimated)
> 	Profiling through timer interrupt
> 	samples  %        app name                 symbol name
> 	1371     31.9879  libpixman.so.1.0.0       fbRasterizeEdges8
> 	788      18.3854  libcairo.so.1.0.0        _cairo_pattern_calc_color_at_pixel
> 	481      11.2226  libpixman.so.1.0.0       IcCombineOverU
> 	356       8.3061  libcairo.so.1.0.0        _cairo_pattern_begin_draw
> 	126       2.9398  libcairo.so.1.0.0        _cairo_pattern_shader_linear
> 	108       2.5198  libpixman.so.1.0.0       IcStepOver
> 	102       2.3798  libpixman.so.1.0.0       pixman_compositeGeneral
> 	89        2.0765  libpixman.so.1.0.0       IcFetch_a8
> 	83        1.9365  libpixman.so.1.0.0       IcOver
> 	79        1.8432  libpixman.so.1.0.0       IcCombineMaskU
> 	... [http://cairographics.org/~cworth/images/gearflowers.oprofile]
> 
> So, the rasterization is topping the list, followed closely by
> gradient computation, and then compositing. It'd be nicer to get some
> callgraph-based sums to better estimate those things, but the prime
> candidates for optimization are obvious enough.

With the sysprof profiler, which does do callgraph-based sums, I get
these results:

   _cairo_pattern_calc_color_at_pixel()            36.86 %
   pixman_composite()                              22.90 %
           (with 17.16% of those in pixman_CompositeGeneral)
   fbRasterizeTrapezoid()                          16.17 %

The percentages are totals, ie. they include children of the
functions. The rasterization times reported by the two profilers are
quite different.

I am using CVS HEAD of cairo and libpixman. The modification I made to
svg2png is bascially this:

-    cairo_set_target_png (cr, png_file, CAIRO_FORMAT_ARGB32, width,
height);
+    cairo_set_target_image (cr, data, CAIRO_FORMAT_ARGB32, width,
height, width);


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