Thursday, September 23, 2010

Visualizing IPC Messages in Fennec

More progress on IPC profiling tools, this time a visualization generator. Here is what happens during loading of cnn.com:


On the left you see Fennec before dougt's prefs optimizing patch, and on the right after it. On both sides, the data is as follows:
  • Each line is a single IPC message. Messages are ordered by send time. The width of the line is how long it took until the message was received. The X axis is linear in time.
  • The Y axis also progresses forward in time (since each line is one message, and they are ordered). But it isn't linear (a lot of short messages will take a lot of vertical space, even though little time passed). The numbers show how much time actually passed. So the Y axis really indicates how many messages have been sent.
  • Colors indicate the type of message: green = http, red = prefs, blue = cookies, black = other.
That patch basically removes all the prefs messages, and the result is a 12% speedup (yay!) There were a lot of prefs messages, and even though they were very short and fast to process, they were synchronous (i.e., blocking).

The visualization tool can also show messages for the child and parent process separately (in the image above, they are all shown together).

Instructions for using it:
  • Apply the patch.
  • Run Fennec with something like this (from $objdir/dist/bin):
    • MOZ_IPC_MESSAGE_LOG=1 MOZ_REDIRECT_CHILD_STDOUT=co MOZ_REDIRECT_CHILD_STDERR=ce ./fennec www.cnn.com &> o
  • Run the visualizer with something like this (you need the Python Imaging Library installed):
    • python ../../../mozilla-central/tools/ipcprof/profiler.py o ce
  • Images should have been created, parent.png, child.png, both.png.
A perhaps more easily viewable image can be found here.

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