Re: Performance notes on background flickering

Nifty.  Metacity has a lot of areas where profiling could probably help
performance, and it's nice that someone has stepped up to figure out a
good way to do that.

Could you create a bug on metacity with your recommendations?


On Mon, 2004-05-03 at 21:06 +0200, Soeren Sandmann Pedersen wrote:
> I have done some measurements on what causes the background flickering
> when you move and resize windows. 
> The measurements were done by the "sysprof" profiler which I have
> recently checked into cvs. That profiler works with a kernel
> module that in every timer interrupt generates a stacktrace for the
> current process and writes that to a file in /proc. A user space program
> then interprets this data and displays it in a GUI. This gives CPU
> usage data on a system-wide basis. The module only works with 2.4
> kernels (feel free to port it and send me patches).
> The measurements were done on a Thinkpad laptop with an i810 chipset
> using 8 of 256 MB as video memory. Before April 22, then GNOME terminal
> would draw itself every time it got a ConfigureNotify event. The
> measurements were done with a newer version that only does that when it
> has a transparent background. Also the version of GTK+ used has a patch
> to not draw behind mapped child windows (available in bug . All text is
> drawn with subpixel smoothing.
> The measurements were done by dragging a gnome terminal around on top of
> several other gnome terminals with lots of text in them (an ls -l).
> Highlights from the profile:
>                 - X                                 48%
>                      RENDER                     15%
>                      ConfigureWindow *          10%
>                      WaitForSomething            2%
>                      CopyArea                    2%
>                      Noise ...
>                         * includes painting background
>                 - Metacity (bluecurve)              35%
>                      meta_frames_expose_event   28%
> The break-down inside metacity looks like this:
>     meta_draw_op_draw_with_env					24.28%
>         draw_op_as_pixbuf()					11.72%
>             meta_gradient_spec_render 				 8.62%
>                 meta_gradient_create_multi_vertical		 7.21%
> 	    scale_and_alpha_pixbuf				 2.68%
>             ...
> 	get_gc_for_primitive					 3.20%
> 	parse_x_position_unchecked				 2.08%
> 	gdk_draw_line						 1.54%
> 	g_object_last_unref					 1.31%
> 	parse_y_position_unchecked                               1.16%
> 	...
> A lot of the drawing on my laptop is not accelerated. On my stationary
> computer with the open source Nvidia driver, X is generally taking a lot
> less CPU. RENDER is still around 12 to 15, so it stands out a bit more
> on the X profile. Metacity is generally using more time than X on that
> computer.
> Note that GTK+ simply doesn't show up on this profile. Different
> profiles where Nautilus windows are dragged over a GEdit instance shows
> more time spent in GTK+, but metacity is still generally the big one,
> depending on theme.
> The biggest inside-GTK+ offender in the GEdit case is Pango, but nothing
> truly dramatic (6-7%). For applications with many widgets, like
> Gnumeric, the GObject signal emission overhead is at 10-15% of the total
> cpu time.
> Improving Metacity is likely to help a lot, for the reasons outlined in
> this mail:
> Basically the repaint lag is going to be proportional to
>         P_a / (M - P_f)
> Where P_a is the time it takes to paint an application, M is the time
> between two mouse events, and P_f is the time it takes to paint the
> frame. So improving metacity (ie. reducing P_f) means a non-linear
> improvement in lagging.
> The mail talks about this in the context of resizing, but it is valid
> for opaque moving too. (And the resizing part of the problem is
> completely fixed by the update counter approch that Havoc suggested. I
> recently sent gtk+ and metacity patches to wm-spec-list and
> gtk-devel-list).
> Of course, COMPOSITE will drown the problem in memory, but that is still
> a bit into the future.
> Improving metacity:
> A metacity theme is basically a tree of drawing operations, and drawing
> a frame is done by traversing this tree. There are simple improvements
> to this traversal that could be done
>         - It generates a GC for each node in the tree. Simple caching
>           should be beneficial here.
>         - It parses expressions over and over. Converting to expression
>           trees should be beneficial
> 	- Caching schemes for pixbufs may be possible
> A different approach is to "compile" the tree into pixmaps. I think it
> is possible for most themes to be compiled into a small number
> of pixmaps and make the frame paint be just blitting those to the
> screen. I think this would essentially make metacity disappear from the
> profile, but it is a relatively big and non-trivial project.
> Søren
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