Marcos Dione added the comment:
Ok, I have a preliminary version of the patch. It has several parts:
* Adding the functionality to the os module, with docstring.
* Make shutil.copyfileobj() to use it if available.
* Modify the docs (this has to be done by hand, right?).
* Modify NEWS and ACKS.
Several points:
* For the time being, flags must be 0, so I was not sure whether put the
argument or not. Just in case, I put it.
* I'm not sure how to test for availability, so configure defines
HAVE_COPY_FILE_RANGE.
* No tests yet.
Talking about tests, I tried copying a 325MiB on an SSD, f2fs. Here are the
times:
Old user space copy:
$ time ./python -m timeit -n 10 -s 'import shutil' 'a = open ("a.mp4", "rb"); b
= open ("b.mp4", "wb+"); shutil.copyfileobj (a, b, 16*1024*1024)'
10 loops, best of 3: 259 msec per loop
real 0m7.915s
user 0m0.104s
sys 0m7.792s
New copy_file_range:
$ time ./python -m timeit -n 10 -s 'import shutil' 'a = open ("a.mp4", "rb"); b
= open ("b.mp4", "wb+"); shutil.copyfileobj (a, b, 16*1024*1024)'
10 loops, best of 3: 193 msec per loop
real 0m5.926s
user 0m0.080s
sys 0m5.836s
Some 20% improvement, but notice that the buffer size is 1024 times Python's
default size (16MiB vs. 16KiB).
One difference that I notice in semantics is that if the file is not open in
binary form, but the file is binary, you get no UnicodeDecodeError (because the
data never reaches userspace).
Let me know what you think.
----------
keywords: +patch
Added file: http://bugs.python.org/file42616/copy_file_range.diff
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