Mercurial > hg
view tests/test-nointerrupt.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 | 531f5e933e49 |
children | 3ba87d5b9ad3 |
line wrap: on
line source
Dummy extension simulating unsafe long running command $ cat > sleepext.py <<EOF > import itertools > import time > > from mercurial.i18n import _ > from mercurial import registrar > > cmdtable = {} > command = registrar.command(cmdtable) > > @command(b'sleep', [], _(b'TIME'), norepo=True) > def sleep(ui, sleeptime=b"1", **opts): > with ui.uninterruptable(): > for _i in itertools.repeat(None, int(sleeptime)): > time.sleep(1) > ui.warn(b"end of unsafe operation\n") > ui.warn(b"%s second(s) passed\n" % sleeptime) > EOF Kludge to emulate timeout(1) which is not generally available. $ cat > timeout.py <<EOF > from __future__ import print_function > import argparse > import signal > import subprocess > import sys > import time > > ap = argparse.ArgumentParser() > ap.add_argument('-s', nargs=1, default='SIGTERM') > ap.add_argument('duration', nargs=1, type=int) > ap.add_argument('argv', nargs='*') > opts = ap.parse_args() > try: > sig = int(opts.s[0]) > except ValueError: > sname = opts.s[0] > if not sname.startswith('SIG'): > sname = 'SIG' + sname > sig = getattr(signal, sname) > proc = subprocess.Popen(opts.argv) > time.sleep(opts.duration[0]) > proc.poll() > if proc.returncode is None: > proc.send_signal(sig) > proc.wait() > sys.exit(124) > EOF Set up repository $ hg init repo $ cd repo $ cat >> $HGRCPATH << EOF > [extensions] > sleepext = ../sleepext.py > EOF Test ctrl-c $ python $TESTTMP/timeout.py -s INT 1 hg sleep 2 interrupted! [124] $ cat >> $HGRCPATH << EOF > [experimental] > nointerrupt = yes > EOF $ python $TESTTMP/timeout.py -s INT 1 hg sleep 2 interrupted! [124] $ cat >> $HGRCPATH << EOF > [experimental] > nointerrupt-interactiveonly = False > EOF $ python $TESTTMP/timeout.py -s INT 1 hg sleep 2 shutting down cleanly press ^C again to terminate immediately (dangerous) end of unsafe operation interrupted! [124]