Mercurial > hg
view contrib/base-revsets.txt @ 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 | 70a4289896b0 |
children | a4483e380c3e |
line wrap: on
line source
# Base Revsets to be used with revsetbenchmarks.py script # # The goal of this file is to gather a limited amount of revsets that allow a # good coverage of the internal revsets mechanisms. Revsets included should not # be selected for their individual implementation, but for what they reveal of # the internal implementation of smartsets classes (and their interactions). # # Use and update this file when you change internal implementation of these # smartsets classes. Please include a comment explaining what each of your # addition is testing. Also check if your changes to the smartset class makes # some of the tests inadequate and replace them with a new one testing the same # behavior. # # If you want to benchmark revsets predicate itself, check 'all-revsets.txt'. # # The current content of this file is currently likely not reaching this goal # entirely, feel free, to audit its content and comment on each revset to # highlight what internal mechanisms they test. all() draft() ::tip draft() and ::tip ::tip and draft() 0::tip roots(0::tip) author(lmoscovicz) author(mpm) author(lmoscovicz) or author(mpm) author(mpm) or author(lmoscovicz) tip:0 0:: # those two `roots(...)` inputs are close to what phase movement use. roots((tip~100::) - (tip~100::tip)) roots((0::) - (0::tip)) 42:68 and roots(42:tip) ::p1(p1(tip)):: public() :10000 and public() draft() :10000 and draft() roots((0:tip)::) (not public() - obsolete()) (_intlist('20000\x0020001')) and merge() parents(20000) (20000::) - (20000) # The one below is used by rebase (children(ancestor(tip~5, tip)) and ::(tip~5)):: heads(commonancestors(last(head(), 2)))