[Python-Dev] Disabling cyclic GC in timeit module (original) (raw)

Steven D'Aprano steve at pearwood.info
Sat Oct 8 02:51:04 CEST 2011

Antoine Pitrou wrote:

In CPython, looking for reference cycles is a parasitic task that interferes with what you are trying to measure. It is not critical in any way, and you can schedule it much less often if it takes too much CPU, without any really adverse consequences. timeit takes the safe way and disables it completely.

In PyPy, it doesn't seem gc.disable() should do anything, since you'd lose all automatic memory management if the GC was disabled. it disables finalizers but this is besides the point. the point is that people use timeit module to compute absolute time it takes for CPython to do things, among other things comparing it to PyPy. While I do agree that in microbenchmarks you don't loose much by just disabling it, it does affect larger applications. So answering the question like "how much time will take json encoding in my application" should take cyclic GC time into account. If you are only measuring json encoding of a few select pieces of data then it's a microbenchmark. If you are measuring the whole application (or a significant part of it) then I'm not sure timeit is the right tool for that.

Perhaps timeit should grow a macro-benchmark tool too? I find myself often using timeit to time macro-benchmarks simply because it's more convenient at the interactive interpreter than the alternatives.

Something like this idea perhaps?

http://preshing.com/20110924/timing-your-code-using-pythons-with-statement

-- Steven

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