[Python-Dev] Disabling cyclic GC in timeit module

[Maciej Fijalkowski]

On Sat, Oct 8, 2011 at 2:18 AM, Antoine Pitrou <solipsis at pitrou.net> 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.
>
> Regards
>
> Antoine.
>

When you're measuring how much time it takes to encode json, this is a
microbenchmark and yet the time that timeit gives you is misleading,
because it'll take different amount of time in your application. I
guess my proposition would be to not disable gc by default and disable
it when requested, but well, I guess I'll give up given the strong
push against it.

Cheers,
fijal