Too Much Context Switching?
talon at lpthe.jussieu.fr
Mon Jun 30 17:15:01 UTC 2008
Kris Kennaway wrote:
> In 6.x. the default thread library is quite inefficient although it can
> make use of multiple CPUs (again, providing the application is giving
> them work to do). For multi-threaded performance you will be better off
> switching to the libthr library (see libmap.conf(5)) or updating to 7.0
> (where it is the default). This isn't likely to be the underlying issue
> if you are trying to debug a loss of performance relative to the same
> configuration in the past though.
Indeed Plone is written in python, and python has a "Big Giant Lock"
inside which insures that only one thread can execute, in order to
protect the python structures. This lock is only released under special
circumstances, such as doing IO. Hence it is necessary to run several
instances of python programs and do synchronization work, if one wants
to make use of several CPUs, or use python threads, and immediately make
some IOs, or similar techniques. It may be that using Jython, if
possible, yields better threading behavior. When doing some work
according to these ideas, i had found quite severe contention, and this
was not cured when switching native threading libraries (libksd, libthr,
etc.). The problem is really inside python.
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