Mercurial > hg
view tests/test-parseindex.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 | f0fadc5bea21 |
children | 828a45233036 |
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revlog.parseindex must be able to parse the index file even if an index entry is split between two 64k blocks. The ideal test would be to create an index file with inline data where 64k < size < 64k + 64 (64k is the size of the read buffer, 64 is the size of an index entry) and with an index entry starting right before the 64k block boundary, and try to read it. We approximate that by reducing the read buffer to 1 byte. $ hg init a $ cd a $ echo abc > foo $ hg add foo $ hg commit -m 'add foo' $ echo >> foo $ hg commit -m 'change foo' $ hg log -r 0: changeset: 0:7c31755bf9b5 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: add foo changeset: 1:26333235a41c tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: change foo $ cat >> test.py << EOF > from __future__ import print_function > from mercurial import changelog, vfs > from mercurial.node import * > > class singlebyteread(object): > def __init__(self, real): > self.real = real > > def read(self, size=-1): > if size == 65536: > size = 1 > return self.real.read(size) > > def __getattr__(self, key): > return getattr(self.real, key) > > def __enter__(self): > self.real.__enter__() > return self > > def __exit__(self, *args, **kwargs): > return self.real.__exit__(*args, **kwargs) > > def opener(*args): > o = vfs.vfs(*args) > def wrapper(*a, **kwargs): > f = o(*a, **kwargs) > return singlebyteread(f) > return wrapper > > cl = changelog.changelog(opener('.hg/store')) > print(len(cl), 'revisions:') > for r in cl: > print(short(cl.node(r))) > EOF $ $PYTHON test.py 2 revisions: 7c31755bf9b5 26333235a41c $ cd .. #if no-pure Test SEGV caused by bad revision passed to reachableroots() (issue4775): $ cd a $ $PYTHON <<EOF > from __future__ import print_function > from mercurial import changelog, vfs > cl = changelog.changelog(vfs.vfs('.hg/store')) > print('good heads:') > for head in [0, len(cl) - 1, -1]: > print('%s: %r' % (head, cl.reachableroots(0, [head], [0]))) > print('bad heads:') > for head in [len(cl), 10000, -2, -10000, None]: > print('%s:' % head, end=' ') > try: > cl.reachableroots(0, [head], [0]) > print('uncaught buffer overflow?') > except (IndexError, TypeError) as inst: > print(inst) > print('good roots:') > for root in [0, len(cl) - 1, -1]: > print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root]))) > print('out-of-range roots are ignored:') > for root in [len(cl), 10000, -2, -10000]: > print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root]))) > print('bad roots:') > for root in [None]: > print('%s:' % root, end=' ') > try: > cl.reachableroots(root, [len(cl) - 1], [root]) > print('uncaught error?') > except TypeError as inst: > print(inst) > EOF good heads: 0: [0] 1: [0] -1: [] bad heads: 2: head out of range 10000: head out of range -2: head out of range -10000: head out of range None: an integer is required good roots: 0: [0] 1: [1] -1: [-1] out-of-range roots are ignored: 2: [] 10000: [] -2: [] -10000: [] bad roots: None: an integer is required $ cd .. Test corrupted p1/p2 fields that could cause SEGV at parsers.c: $ mkdir invalidparent $ cd invalidparent $ hg clone --pull -q --config phases.publish=False ../a limit $ hg clone --pull -q --config phases.publish=False ../a segv $ rm -R limit/.hg/cache segv/.hg/cache $ $PYTHON <<EOF > data = open("limit/.hg/store/00changelog.i", "rb").read() > for n, p in [(b'limit', b'\0\0\0\x02'), (b'segv', b'\0\x01\0\0')]: > # corrupt p1 at rev0 and p2 at rev1 > d = data[:24] + p + data[28:127 + 28] + p + data[127 + 32:] > open(n + b"/.hg/store/00changelog.i", "wb").write(d) > EOF $ hg -R limit debugindex -f1 -c rev flag size link p1 p2 nodeid 0 0000 62 0 2 -1 7c31755bf9b5 1 0000 65 1 0 2 26333235a41c $ hg -R limit debugdeltachain -c rev chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio 0 1 1 -1 base 63 62 63 1.01613 63 0 0.00000 1 2 1 -1 base 66 65 66 1.01538 66 0 0.00000 $ hg -R segv debugindex -f1 -c rev flag size link p1 p2 nodeid 0 0000 62 0 65536 -1 7c31755bf9b5 1 0000 65 1 0 65536 26333235a41c $ hg -R segv debugdeltachain -c rev chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio 0 1 1 -1 base 63 62 63 1.01613 63 0 0.00000 1 2 1 -1 base 66 65 66 1.01538 66 0 0.00000 $ cat <<EOF > test.py > from __future__ import print_function > import sys > from mercurial import changelog, vfs > cl = changelog.changelog(vfs.vfs(sys.argv[1])) > n0, n1 = cl.node(0), cl.node(1) > ops = [ > ('reachableroots', > lambda: cl.index.reachableroots2(0, [1], [0], False)), > ('compute_phases_map_sets', lambda: cl.computephases([[0], []])), > ('index_headrevs', lambda: cl.headrevs()), > ('find_gca_candidates', lambda: cl.commonancestorsheads(n0, n1)), > ('find_deepest', lambda: cl.ancestor(n0, n1)), > ] > for l, f in ops: > print(l + ':', end=' ') > try: > f() > print('uncaught buffer overflow?') > except ValueError as inst: > print(inst) > EOF $ $PYTHON test.py limit/.hg/store reachableroots: parent out of range compute_phases_map_sets: parent out of range index_headrevs: parent out of range find_gca_candidates: parent out of range find_deepest: parent out of range $ $PYTHON test.py segv/.hg/store reachableroots: parent out of range compute_phases_map_sets: parent out of range index_headrevs: parent out of range find_gca_candidates: parent out of range find_deepest: parent out of range $ cd .. #endif