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merge: mark file gets as not thread safe (issue5933)...
merge: mark file gets as not thread safe (issue5933) In default installs, this has the effect of disabling the thread-based worker on Windows when manifesting files in the working directory. My measurements have shown that with revlog-based repositories, Mercurial spends a lot of CPU time in revlog code resolving file data. This ends up incurring a lot of context switching across threads and slows down `hg update` operations when going from an empty working directory to the tip of the repo. On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs): before: 487s wall after: 360s wall (equivalent to worker.enabled=false) cpus=2: 379s wall Even with only 2 threads, the thread pool is still slower. The introduction of the thread-based worker (02b36e860e0b) states that it resulted in a "~50%" speedup for `hg sparse --enable-profile` and `hg sparse --disable-profile`. This disagrees with my measurement above. I theorize a few reasons for this: 1) Removal of files from the working directory is I/O - not CPU - bound and should benefit from a thread pool (unless I/O is insanely fast and the GIL release is near instantaneous). So tests like `hg sparse --enable-profile` may exercise deletion throughput and aren't good benchmarks for worker tasks that are CPU heavy. 2) The patch was authored by someone at Facebook. The results were likely measured against a repository using remotefilelog. And I believe that revision retrieval during working directory updates with remotefilelog will often use a remote store, thus being I/O and not CPU bound. This probably resulted in an overstated performance gain. Since there appears to be a need to enable the thread-based worker with some stores, I've made the flagging of file gets as thread safe configurable. I've made it experimental because I don't want to formalize a boolean flag for this option and because this attribute is best captured against the store implementation. But we don't have a proper store API for this yet. I'd rather cross this bridge later. It is possible there are revlog-based repositories that do benefit from a thread-based worker. I didn't do very comprehensive testing. If there are, we may want to devise a more proper algorithm for whether to use the thread-based worker, including possibly config options to limit the number of threads to use. But until I see evidence that justifies complexity, simplicity wins. Differential Revision: https://phab.mercurial-scm.org/D3963
Sushil khanchi - - Load All Authors

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test-histedit-no-backup.t
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$ . "$TESTDIR/histedit-helpers.sh"
Enable extension used by this test
$ cat >>$HGRCPATH <<EOF
> [extensions]
> histedit=
> EOF
Repo setup:
$ hg init foo
$ cd foo
$ echo first>file
$ hg ci -qAm one
$ echo second>>file
$ hg ci -m two
$ echo third>>file
$ hg ci -m three
$ echo forth>>file
$ hg ci -m four
$ hg log -G --style compact
@ 3[tip] 7d5187087c79 1970-01-01 00:00 +0000 test
| four
|
o 2 80d23dfa866d 1970-01-01 00:00 +0000 test
| three
|
o 1 6153eb23e623 1970-01-01 00:00 +0000 test
| two
|
o 0 36b4bdd91f5b 1970-01-01 00:00 +0000 test
one
Check when --no-backup is not passed
$ hg histedit -r '36b4bdd91f5b' --commands - << EOF
> pick 36b4bdd91f5b 0 one
> pick 6153eb23e623 1 two
> roll 80d23dfa866d 2 three
> edit 7d5187087c79 3 four
> EOF
merging file
Editing (7d5187087c79), you may commit or record as needed now.
(hg histedit --continue to resume)
[1]
$ hg histedit --abort
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
saved backup bundle to $TESTTMP/foo/.hg/strip-backup/1d8f701c7b35-cf7be322-backup.hg
saved backup bundle to $TESTTMP/foo/.hg/strip-backup/5c0056670bce-b54b65d0-backup.hg
$ hg st
$ hg diff
$ hg log -G --style compact
@ 3[tip] 7d5187087c79 1970-01-01 00:00 +0000 test
| four
|
o 2 80d23dfa866d 1970-01-01 00:00 +0000 test
| three
|
o 1 6153eb23e623 1970-01-01 00:00 +0000 test
| two
|
o 0 36b4bdd91f5b 1970-01-01 00:00 +0000 test
one
Check when --no-backup is passed
$ hg histedit -r '36b4bdd91f5b' --commands - << EOF
> pick 36b4bdd91f5b 0 one
> pick 6153eb23e623 1 two
> roll 80d23dfa866d 2 three
> edit 7d5187087c79 3 four
> EOF
merging file
Editing (7d5187087c79), you may commit or record as needed now.
(hg histedit --continue to resume)
[1]
$ hg histedit --abort --no-backup
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg st
$ hg diff
$ hg log -G --style compact
@ 3[tip] 7d5187087c79 1970-01-01 00:00 +0000 test
| four
|
o 2 80d23dfa866d 1970-01-01 00:00 +0000 test
| three
|
o 1 6153eb23e623 1970-01-01 00:00 +0000 test
| two
|
o 0 36b4bdd91f5b 1970-01-01 00:00 +0000 test
one