[RFC] dirstate walk speedup
bos at serpentine.com
Fri Sep 28 01:44:13 CDT 2007
This patch speeds up dirstate walk performance substantially.
Here are some timings on a current kernel tree (22529 files), from my
laptop running 2.6.22. Numbers courtesy of "hg --time st".
TREE COLD SPEEDUP WARM SPEEDUP
crew 4.62 0% 0.90 0%
fallback 4.38 5% 0.78 13%
normal 4.18 10% 0.59 35%
The patch simply replaces calls to os.listdir with calls to
osutil.listdir, which stats directory entries as soon as it does a readdir.
There are two versions of the osutil module: a pure Python version,
which is still faster than the current code that calls os.listdir
directly, and a C extension module that does a few extra tricks: it
doesn't call lstat at all if it can avoid it, and it calls fstatat
instead of lstat if available, reducing dentry lookups.
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