Mercurial > hg
view mercurial/help/dates.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 | 7bec3f697d76 |
children |
line wrap: on
line source
Some commands allow the user to specify a date, e.g.: - backout, commit, import, tag: Specify the commit date. - log, revert, update: Select revision(s) by date. Many date formats are valid. Here are some examples: - ``Wed Dec 6 13:18:29 2006`` (local timezone assumed) - ``Dec 6 13:18 -0600`` (year assumed, time offset provided) - ``Dec 6 13:18 UTC`` (UTC and GMT are aliases for +0000) - ``Dec 6`` (midnight) - ``13:18`` (today assumed) - ``3:39`` (3:39AM assumed) - ``3:39pm`` (15:39) - ``2006-12-06 13:18:29`` (ISO 8601 format) - ``2006-12-6 13:18`` - ``2006-12-6`` - ``12-6`` - ``12/6`` - ``12/6/6`` (Dec 6 2006) - ``today`` (midnight) - ``yesterday`` (midnight) - ``now`` - right now Lastly, there is Mercurial's internal format: - ``1165411109 0`` (Wed Dec 6 13:18:29 2006 UTC) This is the internal representation format for dates. The first number is the number of seconds since the epoch (1970-01-01 00:00 UTC). The second is the offset of the local timezone, in seconds west of UTC (negative if the timezone is east of UTC). The log command also accepts date ranges: - ``<DATE`` - at or before a given date/time - ``>DATE`` - on or after a given date/time - ``DATE to DATE`` - a date range, inclusive - ``-DAYS`` - within a given number of days of today