view tests/test-narrow-clone-nonlinear.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

Testing narrow clones when changesets modifying a matching file exist on
multiple branches

  $ . "$TESTDIR/narrow-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF

  $ hg branch default
  marked working directory as branch default
  (branches are permanent and global, did you want a bookmark?)
  $ for x in `$TESTDIR/seq.py 10`; do
  >   echo $x > "f$x"
  >   hg add "f$x"
  >   hg commit -m "Add $x"
  > done

  $ hg branch release-v1
  marked working directory as branch release-v1
  (branches are permanent and global, did you want a bookmark?)
  $ hg commit -m "Start release for v1"

  $ hg update default
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ for x in `$TESTDIR/seq.py 10`; do
  >   echo "$x v2" > "f$x"
  >   hg commit -m "Update $x to v2"
  > done

  $ hg update release-v1
  10 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch release-v1
  marked working directory as branch release-v1
  $ for x in `$TESTDIR/seq.py 1 5`; do
  >   echo "$x v1 hotfix" > "f$x"
  >   hg commit -m "Hotfix $x in v1"
  > done

  $ hg update default
  10 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch release-v2
  marked working directory as branch release-v2
  $ hg commit -m "Start release for v2"

  $ hg update default
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch default
  marked working directory as branch default
  $ for x in `$TESTDIR/seq.py 10`; do
  >   echo "$x v3" > "f$x"
  >   hg commit -m "Update $x to v3"
  > done

  $ hg update release-v2
  10 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch release-v2
  marked working directory as branch release-v2
  $ for x in `$TESTDIR/seq.py 4 9`; do
  >   echo "$x v2 hotfix" > "f$x"
  >   hg commit -m "Hotfix $x in v2"
  > done

  $ hg heads -T '{rev} <- {p1rev} ({branch}): {desc}\n'
  42 <- 41 (release-v2): Hotfix 9 in v2
  36 <- 35 (default): Update 10 to v3
  25 <- 24 (release-v1): Hotfix 5 in v1

  $ cd ..

We now have 3 branches: default, which has v3 of all files, release-v1 which
has v1 of all files, and release-v2 with v2 of all files.

Narrow clone which should get all branches

  $ hg clone --narrow ssh://user@dummy/master narrow --include "f5"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 12 changesets with 5 changes to 1 files (+2 heads)
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ hg log -G -T "{if(ellipsis, '...')}{node|short} ({branch}): {desc}\n"
  o  ...031f516143fe (release-v2): Hotfix 9 in v2
  |
  o  9cd7f7bb9ca1 (release-v2): Hotfix 5 in v2
  |
  o  ...37bbc88f3ef0 (release-v2): Hotfix 4 in v2
  |
  | @  ...dae2f368ca07 (default): Update 10 to v3
  | |
  | o  9c224e89cb31 (default): Update 5 to v3
  | |
  | o  ...04fb59c7c9dc (default): Update 4 to v3
  |/
  | o  b2253e82401f (release-v1): Hotfix 5 in v1
  | |
  | o  ...960ac37d74fd (release-v1): Hotfix 4 in v1
  | |
  o |  986298e3f347 (default): Update 5 to v2
  | |
  o |  ...75d539c667ec (default): Update 4 to v2
  |/
  o  04c71bd5707f (default): Add 5
  |
  o  ...881b3891d041 (default): Add 4
  

Narrow clone the first file, hitting edge condition where unaligned
changeset and manifest revnums cross branches.

  $ hg clone --narrow ssh://user@dummy/master narrow --include "f1"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 10 changesets with 4 changes to 1 files (+2 heads)
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ hg log -G -T "{if(ellipsis, '...')}{node|short} ({branch}): {desc}\n"
  o  ...031f516143fe (release-v2): Hotfix 9 in v2
  |
  | @  ...dae2f368ca07 (default): Update 10 to v3
  | |
  | o  1f5d184b8e96 (default): Update 1 to v3
  |/
  | o  ...b2253e82401f (release-v1): Hotfix 5 in v1
  | |
  | o  133502f6b7e5 (release-v1): Hotfix 1 in v1
  | |
  o |  ...79165c83d644 (default): Update 10 to v2
  | |
  o |  c7b7a5f2f088 (default): Update 1 to v2
  | |
  | o  ...f0531a3db7a9 (release-v1): Start release for v1
  |/
  o  ...6a3f0f0abef3 (default): Add 10
  |
  o  e012ac15eaaa (default): Add 1