[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[STINNER Victor]

STINNER Victor  added the comment:

Try maybe PYTHONPROFILEIMPORTTIME=1 env var to get stats on impots.

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[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[Zachary Ware]

Zachary Ware  added the comment:

I've finally had a chance to try to reproduce this myself, and did.  However, a 
subsequent run of `test.exe` showed exactly the same timing as the Python test, 
and even another attempt after removing and re-installing tensorflow showed 
comparable timing to the Python version.  Can you reproduce the slow timing on 
multiple runs?

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[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[deekay]

deekay  added the comment:

The times are correct. It's very noticeable even without using a stopwatch. The 
C version actually takes 23 seconds to execute.

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[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[Zachary Ware]

Zachary Ware  added the comment:

Are you quite sure you're converting your times correctly, particularly in the 
C code?  The units in the Python version should be seconds; does the C version 
actually take 23 seconds to execute?  What kind of timing do you get if you 
time both programs with the same external program?

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[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[Andy Lester]

Change by Andy Lester :


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[issue40314] python code order of magnitude faster than equivalent CPython code for simple import statement

[deekay]

New submission from deekay :

I'm baffled by the performance difference of the following two semantically 
equivalent(?) programs.

Python:

#test.py
import time
starttime=time.time()
import tensorflow 
print(f"Import took: {time.time() - starttime}")

vs C using CPython

//test.c
#include 
#include  
#include  
int main(int argc, char *argv[])
{
Py_Initialize();
clock_t t = clock();
PyObject* pModule = PyImport_ImportModule("tensorflow");
double time_taken = ((double)clock() - t)/CLOCKS_PER_SEC;
printf("Import took:  %f\n", time_taken);
return 0;
}

Now compare the two:

cl.exe /I"C:\Program Files\Python37\include" test.c
link test.obj python37.lib /LIBPATH:"C:\Program Files\Python37\libs"
.\test.exe


> 2020-04-17 13:00:51.598550: W 
> tensorflow/stream_executor/platform/default/dso_loader.cc:55] Could not load 
> dynamic library 'cudart64_100.dll'; dlerror: cudart64_100.dll not found
> 2020-04-17 13:00:51.606296: I 
> tensorflow/stream_executor/cuda/cudart_stub.cc:29] Ignore above cudart 
> dlerror if you do not have a GPU set up on your machine.

> **Import took: 23.160523891448975**


python test.py


> 2020-04-17 13:01:19.525648: W 
> tensorflow/stream_executor/platform/default/dso_loader.cc:55] Could not load 
> dynamic library 'cudart64_100.dll'; dlerror: cudart64_100.dll not found
> 2020-04-17 13:01:19.530726: I 
> tensorflow/stream_executor/cuda/cudart_stub.cc:29] Ignore above cudart 
> dlerror if you do not have a GPU set up on your machine.

> **Import took: 2.3172824382781982**


Not that it should matter much but my tensorflow version is 1.15
Why is the python VM code so much faster than the compiled CPython code?
Does the python vm add some magic that PyImport_ImportModule doesn't?

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components: C API
messages: 366683
nosy: deekay
priority: normal
severity: normal
status: open
title: python code order of magnitude faster than equivalent CPython code for 
simple import statement
versions: Python 3.7

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