perf: add threading capability to perfbdiff
Since we are releasing the GIL during diffing, it is interesting to see how a
thread pool would perform on diffing. We add a new `--threads` argument to
commands. Synchronizing the thread pool is a bit complex because we want to be
able to reuse it from one run to another.
On my computer (i7 with 4 cores + hyperthreading), I get the following data for
about 12000 revisions:
threads wall comb wall gain comb overhead
none 31.596715 31.59 0.00% 0.00%
1 31.621228 31.62 -0.08% 0.09%
2 16.406202 32.8 48.08% 3.83%
3 11.598334 34.76 63.29% 10.03%
4 9.205421 36.77 70.87% 16.40%
5 8.517604 42.51 73.04% 34.57%
6 7.94645 47.58 74.85% 50.62%
7 7.434972 51.92 76.47% 64.36%
8 7.070638 55.34 77.62% 75.18%
Compared to the feature disabled (threads=0), the overhead is negligible with
the threading code (threads=1), and the gain is already 48% with two threads.
#require bzr bzr114
$ . "$TESTDIR/bzr-definitions"
The file/directory replacement can only be reproduced on
bzr >= 1.4. Merge it back in test-convert-bzr-directories once
this version becomes mainstream.
replace file with dir
$ mkdir test-replace-file-with-dir
$ cd test-replace-file-with-dir
$ bzr init -q source
$ cd source
$ echo d > d
$ bzr add -q d
$ bzr commit -q -m 'add d file'
$ rm d
$ mkdir d
$ bzr add -q d
$ bzr commit -q -m 'replace with d dir'
$ echo a > d/a
$ bzr add -q d/a
$ bzr commit -q -m 'add d/a'
$ cd ..
$ hg convert source source-hg
initializing destination source-hg repository
scanning source...
sorting...
converting...
2 add d file
1 replace with d dir
0 add d/a
$ manifest source-hg tip
% manifest of tip
644 d/a
$ cd source-hg
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd ../..