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Slow tarfile extract on armv7l Linux machine

Hi, I'm seeing a very slow extraction of an uncompressed tar file using 
'tarfile' in Python 3.5.3 vs. the native Debian tar tool. This is a 
console log from my machine:

jimm at scw-000001:~$ time tar xf update.tar

real??? 0m3.436s
user??? 0m0.430s
sys???? 0m2.870s
jimm at scw-000001:~$ rm -rf home
jimm at scw-000001:~$ cat untar-test.py
#!/usr/bin/env python3

import tarfile

tar = tarfile.open('update.tar')


jimm at scw-000001:~$ time ./untar-test.py

real??? 0m12.216s
user??? 0m8.730s
sys???? 0m3.030s
jimm at scw-000001:~$ uname -a
Linux scw-000001 4.3.5-std-1 #1 SMP Fri Feb 19 11:52:18 UTC 2016 armv7l 
jimm at scw-000001:~$ python3
Python 3.5.3 (default, Jan 19 2017, 14:11:04)
[GCC 6.3.0 20170118] on linux
Type "help", "copyright", "credits" or "license" for more information.


I also tried this with 3.7.0b3 and I get the same result. On my desktop, 
an x86_64 running Ubuntu, there's little difference between tarfile and 
native tar. Obviously there will be some time spent starting Python but 
the above seems too much. Does anyone have any ideas what might cause 
this or where to look next? Does x86_64 do more of this in C code that's 
interpreted on armv7l, for example?