[issue38541] Performance degradation of attribute accesses in Python 3.7.4

[Irit Katriel]

Irit Katriel  added the comment:

Closing as this is resolved in 3.8 and we won't do anything about 3.7.

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nosy: +iritkatriel
resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue38541] Performance degradation of attribute accesses in Python 3.7.4

[ttrd]

ttrd  added the comment:

I just ran the test with Python 3.7.5: As expected, I got the same results as 
in Python 3.7.4.

Nevertheless, thanks for the response. So we will stay with Python 3.7.3 for 
now and switch to Python 3.8 as soon as possible.

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[issue38541] Performance degradation of attribute accesses in Python 3.7.4

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I added a note to #28866 about this.  The fix in #36922 is likely an 
enhancement that cannot be backported.  Please retest with 3.7.5 if you can, 
though I have no expectation of any change.

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nosy: +serhiy.storchaka, terry.reedy

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[issue38541] Performance degradation of attribute accesses in Python 3.7.4

[ttrd]

New submission from ttrd :

After upgrading from Python 3.7.3 to Python 3.7.4, we noticed an increased 
runtime of about 50% in some tests of our application.

After some testing we constructed the following hypothesis: Accessing instance 
attributes of classes that define a custom metaclass take more time in Python 
3.7.4. The access takes the more time the more classes are in the MRO of the 
concerning class (in other words the more base classes the concerning class has 
got).

We verified the hypothesis by creating a minimal example (file attached) that 
produced the output at the bottom. (The index defines the number of base 
classes. The four variants are with/without a metaclass and with 
simple/multiple inheritance. The kind of inheritance has no influence on the 
runtime.)

In Python 3.7.4 (in contrast to 3.7.3 and 3.8), you can see that the usage of a 
metaclass results in a linear increase of the runtime of attribute accesses 
depending on the number of base classes.

We could also identify the issue/commit that introduced the performance issue:
https://bugs.python.org/issue28866
https://github.com/python/cpython/commit/bfd0b7720196b9ff647cc33dafbd31a04496402c

In the Python 3.8 branch, the performance issue seems to be resolved by:
https://bugs.python.org/issue36922
https://github.com/python/cpython/commit/988fff5d0e7fccecbf776c08ec56695820b3b4a8

Will this performance issue be addressed in a future 3.7 version (e.g. 3.7.6) 
or is it in your optinion sufficient that the issue seems to be resolved in 3.8?


Python 3.7.3 (constant runtime)

3.668036e-08 noMetaBaseX[1].attr
3.630355e-08 noMetaBaseX[2].attr
3.687350e-08 noMetaBaseX[5].attr
3.827102e-08 noMetaBaseX[10].attr
3.724956e-08 noMetaBaseX[20].attr
3.912778e-08 noMetaBaseX[50].attr
4.072552e-08 noMetaBaseX[100].attr
3.620875e-08 metaBaseX[1].attr
3.640054e-08 metaBaseX[2].attr
3.599339e-08 metaBaseX[5].attr
3.606570e-08 metaBaseX[10].attr
3.946514e-08 metaBaseX[20].attr
3.715085e-08 metaBaseX[50].attr
3.762364e-08 metaBaseX[100].attr
3.667802e-08 noMetaRecBaseX[1].attr
3.579415e-08 noMetaRecBaseX[2].attr
3.647997e-08 noMetaRecBaseX[5].attr
3.577428e-08 noMetaRecBaseX[10].attr
3.686319e-08 noMetaRecBaseX[20].attr
3.832261e-08 noMetaRecBaseX[50].attr
4.087625e-08 noMetaRecBaseX[100].attr
3.654509e-08 noMetaRecBaseX[1].attr
3.617825e-08 noMetaRecBaseX[2].attr
3.573970e-08 noMetaRecBaseX[5].attr
3.664559e-08 noMetaRecBaseX[10].attr
3.702526e-08 noMetaRecBaseX[20].attr
3.774067e-08 noMetaRecBaseX[50].attr
3.836915e-08 noMetaRecBaseX[100].attr

Python 3.7.4 (see lines marked with ->)

4.042378e-08 noMetaBaseX[1].attr
3.704071e-08 noMetaBaseX[2].attr
3.868766e-08 noMetaBaseX[5].attr
3.716869e-08 noMetaBaseX[10].attr
3.693100e-08 noMetaBaseX[20].attr
3.947849e-08 noMetaBaseX[50].attr
3.790146e-08 noMetaBaseX[100].attr
-> 5.010019e-08 metaBaseX[1].attr
-> 5.215336e-08 metaBaseX[2].attr
-> 6.103393e-08 metaBaseX[5].attr
-> 7.947347e-08 metaBaseX[10].attr
-> 1.082155e-07 metaBaseX[20].attr
-> 2.264330e-07 metaBaseX[50].attr
-> 4.951039e-07 metaBaseX[100].attr
3.727378e-08 noMetaRecBaseX[1].attr
3.815971e-08 noMetaRecBaseX[2].attr
3.661390e-08 noMetaRecBaseX[5].attr
3.709824e-08 noMetaRecBaseX[10].attr
3.785757e-08 noMetaRecBaseX[20].attr
3.813983e-08 noMetaRecBaseX[50].attr
3.856352e-08 noMetaRecBaseX[100].attr
-> 5.260115e-08 metaRecBaseX[1].attr
-> 5.661043e-08 metaRecBaseX[2].attr
-> 6.760995e-08 metaRecBaseX[5].attr
-> 8.038124e-08 metaRecBaseX[10].attr
-> 1.100538e-07 metaRecBaseX[20].attr
-> 2.246786e-07 metaRecBaseX[50].attr
-> 4.877147e-07 metaRecBaseX[100].attr

​Python 3.8.0rc1 (constant runtime)

​4.045787e-08 noMetaBaseX[1].attr
4.206206e-08 noMetaBaseX[2].attr
4.209608e-08 noMetaBaseX[5].attr
4.049552e-08 noMetaBaseX[10].attr
4.133343e-08 noMetaBaseX[20].attr
4.229599e-08 noMetaBaseX[50].attr
4.259420e-08 noMetaBaseX[100].attr
4.146996e-08 metaBaseX[1].attr
4.140459e-08 metaBaseX[2].attr
4.143048e-08 metaBaseX[5].attr
4.054639e-08 metaBaseX[10].attr
4.219960e-08 metaBaseX[20].attr
4.222810e-08 metaBaseX[50].attr
4.420123e-08 metaBaseX[100].attr
4.044410e-08 noMetaRecBaseX[1].attr
4.043790e-08 noMetaRecBaseX[2].attr
4.209061e-08 noMetaRecBaseX[5].attr
4.042041e-08 noMetaRecBaseX[10].attr
4.048202e-08 noMetaRecBaseX[20].attr
4.260607e-08 noMetaRecBaseX[50].attr
4.267928e-08 noMetaRecBaseX[100].attr
4.037958e-08 metaRecBaseX[1].attr
3.968827e-08 metaRecBaseX[2].attr
4.011758e-08 metaRecBaseX[5].attr
3.954960e-08 metaRecBaseX[10].attr
4.057979e-08 metaRecBaseX[20].attr
4.145640e-08 metaRecBaseX[50].attr
4.148783e-08 metaRecBaseX[100].attr

--
components: Interpreter Core
files: timeAttrAccess.py
messages: 355029
nosy: ttrd
priority: normal
severity: normal
status: open
title: Performance degradation of attribute accesses in Python 3.7.4
type: performance
versions: Python 3.7
Added file: https://bugs.python.org/file48670/timeAttrAccess.py

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