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= Hacker's guide to WebKit/GTK+ =

== Optimization ==

Little work has yet been done to optimize the GTK+ port so there's plenty of low-hanging fruit. There's a "Performance" tag in the bug tracker which should be used for performance-related bugs.

=== Dependencies ===

WebKit/GTK+ performance characteristics are highly dependent on the platform environment:

 * Recent versions of Cairo are essential for good performance. Was developed tracking Cairo git head.
 * X server configuration: Does the device have accelerated blitting, scaling or more?

=== Tools ===

 * Web-based
  * JavaScript
   * http://webkit.org/perf/sunspider-0.9/sunspider.html
   * http://celtickane.com/webdesign/jsspeed2007.php
   * http://en.wikipedia.org/wiki/IBench
 * Local
  * Already used successfully in WebKit/GTK+ optimization
   * gperf
   * xrestop
   * callgrind (of valgrind)
  * Not yet tried
   * oprofile

== Speculation ==

=== Graphics ===

 * There is no back-buffer -- everything is redrawn on every scroll. It's actually kind of impressive that the browser is still usable despite all the needless re-drawing.
 * All image rendering is done client-side rather than being uploaded to the X server. Not great, but not a big issue (and maybe even a small win) on devices without good hardware acceleration eg. N800.

=== SVG ===

 * Many mallocs that could be done on the stack.
 * Hit-testing slowness. Was discussed on the Cairo list around Nov '07. Gecko guys are tracking this one too.

=== Canvas ===

 * Lots of going back-and-forth between system and video memory from what I can tell. Could do something smarter here.

=== CURL http ===

 * Suspicions that we are blocking the main thread too long here. Some kind of main loop integration (code is readily available for this, [http://atterer.net/glibcurl/ glibcurl]) will help, but should probably be integrated only after the existing code is cleaned up.
 * http cache: There is none.

=== Image decoders ===

 * Potential for memory reductions (TODO: add bug# here)

== Comparative ==

=== Nokia internet tablets ===

This applies to perf testing on the N770, N800 and N810.

Test the browser as displayed normally (ie. not full screen, not minimised).

I run tests with no applications other than a single xterm in the background.

Power saving:

 * Disable power saving to avoid CPU/tick scaling after a period of inactivity
  * Control panel -> Display -> Display stays lit: When charging
  * Keep it plugged in

If benchmarking Gecko-based browsers like MicroB:

 * Go to about:config, set dom.max_script_run_time to 0