Mercurial > hg
view tests/test-mq-symlinks.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
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | c2380b448265 |
children | 55c6ebd11cb9 |
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#require symlink $ echo "[extensions]" >> $HGRCPATH $ echo "mq=" >> $HGRCPATH $ hg init $ hg qinit $ hg qnew base.patch $ echo aaa > a $ echo bbb > b $ echo ccc > c $ hg add a b c $ hg qrefresh $ readlink.py a a -> a not a symlink test replacing a file with a symlink $ hg qnew symlink.patch $ rm a $ ln -s b a $ hg qrefresh --git $ readlink.py a a -> b $ hg qpop popping symlink.patch now at: base.patch $ hg qpush applying symlink.patch now at: symlink.patch $ readlink.py a a -> b test updating a symlink $ rm a $ ln -s c a $ hg qnew --git -f updatelink $ readlink.py a a -> c $ hg qpop popping updatelink now at: symlink.patch $ hg qpush --debug applying updatelink patching file a committing files: a committing manifest committing changelog updating the branch cache now at: updatelink $ readlink.py a a -> c $ hg st test replacing a symlink with a file $ ln -s c s $ hg add s $ hg qnew --git -f addlink $ rm s $ echo sss > s $ hg qnew --git -f replacelinkwithfile $ hg qpop popping replacelinkwithfile now at: addlink $ hg qpush applying replacelinkwithfile now at: replacelinkwithfile $ cat s sss $ hg st test symlink removal $ hg qnew removesl.patch $ hg rm a $ hg qrefresh --git $ hg qpop popping removesl.patch now at: replacelinkwithfile $ hg qpush applying removesl.patch now at: removesl.patch $ hg st -c C b C c C s replace broken symlink with another broken symlink $ ln -s linka linka $ hg add linka $ hg qnew link $ hg mv linka linkb $ rm linkb $ ln -s linkb linkb $ hg qnew movelink $ hg qpop popping movelink now at: link $ hg qpush applying movelink now at: movelink $ readlink.py linkb linkb -> linkb