view tests/test-filebranch.t @ 38732:be4984261611

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

This test makes sure that we don't mark a file as merged with its ancestor
when we do a merge.

  $ cat <<EOF > merge
  > from __future__ import print_function
  > import sys, os
  > print("merging for", os.path.basename(sys.argv[1]))
  > EOF
  $ HGMERGE="$PYTHON ../merge"; export HGMERGE

Creating base:

  $ hg init a
  $ cd a
  $ echo 1 > foo
  $ echo 1 > bar
  $ echo 1 > baz
  $ echo 1 > quux
  $ hg add foo bar baz quux
  $ hg commit -m "base"

  $ cd ..
  $ hg clone a b
  updating to branch default
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved

Creating branch a:

  $ cd a
  $ echo 2a > foo
  $ echo 2a > bar
  $ hg commit -m "branch a"

Creating branch b:

  $ cd ..
  $ cd b
  $ echo 2b > foo
  $ echo 2b > baz
  $ hg commit -m "branch b"

We shouldn't have anything but n state here:

  $ hg debugstate --nodates | grep -v "^n"
  [1]

Merging:

  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 2 changes to 2 files (+1 heads)
  new changesets bdd988058d16
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg merge -v
  resolving manifests
  getting bar
  merging foo
  merging for foo
  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ echo 2m > foo
  $ echo 2b > baz
  $ echo new > quux

  $ hg ci -m "merge"

main: we should have a merge here:

  $ hg debugindex --changelog
     rev linkrev nodeid       p1           p2
       0       0 cdca01651b96 000000000000 000000000000
       1       1 f6718a9cb7f3 cdca01651b96 000000000000
       2       2 bdd988058d16 cdca01651b96 000000000000
       3       3 d8a521142a3c f6718a9cb7f3 bdd988058d16

log should show foo and quux changed:

  $ hg log -v -r tip
  changeset:   3:d8a521142a3c
  tag:         tip
  parent:      1:f6718a9cb7f3
  parent:      2:bdd988058d16
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       foo quux
  description:
  merge
  
  

foo: we should have a merge here:

  $ hg debugindex foo
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       1 2ffeddde1b65 b8e02f643373 000000000000
       2       2 33d1fb69067a b8e02f643373 000000000000
       3       3 aa27919ee430 2ffeddde1b65 33d1fb69067a

bar: we should not have a merge here:

  $ hg debugindex bar
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       2 33d1fb69067a b8e02f643373 000000000000

baz: we should not have a merge here:

  $ hg debugindex baz
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       1 2ffeddde1b65 b8e02f643373 000000000000

quux: we should not have a merge here:

  $ hg debugindex quux
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       3 6128c0f33108 b8e02f643373 000000000000

Manifest entries should match tips of all files:

  $ hg manifest --debug
  33d1fb69067a0139622a3fa3b7ba1cdb1367972e 644   bar
  2ffeddde1b65b4827f6746174a145474129fa2ce 644   baz
  aa27919ee4303cfd575e1fb932dd64d75aa08be4 644   foo
  6128c0f33108e8cfbb4e0824d13ae48b466d7280 644   quux

Everything should be clean now:

  $ hg status

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 4 changesets, 10 total revisions

  $ cd ..