Hi Webkittens!
I am planning to turn on the ENABLE_PARALLEL_JOBS feature by default. It
is tracked in https://bugs.webkit.org/show_bug.cgi?id=70032. This
feature has proved to be an efficient optimization for some SVG filters
where it has been applied. Naturally it could be used in other areas as
well in the future. It supports a fork-and-join threading scheme thus it
can be used for computations where the task can be divided to
independent sub-tasks. It plays well with the platform: for Mac it has a
libdispatch based implementation. For other platforms it has a generic
and an openmp based one - the latter is used only in -fopenmp builds.
With the Methanol benchmark - https://gitorious.org/methanol - our
measurements showed a 60% speedup for SVG filters on a 6 core MacPro
(libdispatch implementation) and 40% gain on my 4 core i5 desktop
(generic implementation).
The cost of enabling the feature is a few extra thread creation with the
generic backend. The maximum of thread creations is the number of cores
in the system since the implementation using a basic thread-pool for the
parallel threads. With libdispatch it's cheaper because the system
handles the thread allocation for us. In the case of openmp the cost is
implementation specific but normally it should also has an internal
thread pool. Finally, for !ENABLE(FILTERS) builds there is no cost at
all currently.
Please tell me if you have any concerns about enabling the feature.
-kbalazs
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