tests/test-lock-badness.t

bundle2: increase payload part chunk size to 32kb

Bundle2 payload parts are framed chunks. Esentially, we obtain
data in equal size chunks of size `preferedchunksize` and emit those
to a generator. That generator is fed into a compressor (which can
be the no-op compressor, which just re-emits the generator). And
the output from the compressor likely goes to a file descriptor
or socket.

What this means is that small chunk sizes create more Python objects
and Python function calls than larger chunk sizes. And as we know,
Python object and function call overhead in performance sensitive
code matters (at least with CPython).

This commit increases the bundle2 part payload chunk size from 4k
to 32k. Practically speaking, this means that the chunks we feed
into a compressor (implemented in C code) or feed directly into a
file handle or socket write() are larger. It's possible the chunks
might be larger than what the receiver can handle in one logical
operation. But at that point, we're in C code, which is much more
efficient at dealing with splitting up the chunk and making multiple
function calls than Python is.

A downside to larger chunks is that the receiver has to wait for that
much data to arrive (either raw or from a decompressor) before it
can process the chunk. But 32kb still feels like a small buffer to
have to wait for. And in many cases, the client will convert from
8 read(4096) to 1 read(32768). That's happening in Python land. So
we cut down on the number of Python objects and function calls,
making the client faster as well. I don't think there are any
significant concerns to increasing the payload chunk size to 32kb.

The impact of this change on performance significant. Using `curl`
to obtain a stream clone bundle2 payload from a server on localhost
serving the mozilla-unified repository:

before: 20.78 user; 7.71 system;  80.5 MB/s
after:  13.90 user; 3.51 system; 132 MB/s
legacy:  9.72 user; 8.16 system; 132 MB/s

bundle2 stream clone generation is still more resource intensive than
legacy stream clone (that's likely because of the use of a
util.chunkbuffer). But the throughput is the same. We might
be in territory we're this is effectively a benchmark of the
networking stack or Python's syscall throughput.

From the client perspective, `hg clone -U --stream`:

before: 33.50 user; 7.95 system; 53.3 MB/s
after:  22.82 user; 7.33 system; 72.7 MB/s
legacy: 29.96 user; 7.94 system; 58.0 MB/s

And for `hg clone --stream` with a working directory update of
~230k files:

after:  119.55 user; 26.47 system; 0:57.08 wall
legacy: 126.98 user; 26.94 system; 1:05.56 wall

So, it appears that bundle2's stream clone is now definitively faster
than legacy stream clone!

Differential Revision: https://phab.mercurial-scm.org/D1932

#require unix-permissions no-root no-windows

Prepare

  $ hg init a
  $ echo a > a/a
  $ hg -R a ci -A -m a
  adding a

  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

Test that raising an exception in the release function doesn't cause the lock to choke

  $ cat > testlock.py << EOF
  > from mercurial import error, registrar
  > 
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > 
  > def acquiretestlock(repo, releaseexc):
  >     def unlock():
  >         if releaseexc:
  >             raise error.Abort('expected release exception')
  >     l = repo._lock(repo.vfs, 'testlock', False, unlock, None, 'test lock')
  >     return l
  > 
  > @command(b'testlockexc')
  > def testlockexc(ui, repo):
  >     testlock = acquiretestlock(repo, True)
  >     try:
  >         testlock.release()
  >     finally:
  >         try:
  >             testlock = acquiretestlock(repo, False)
  >         except error.LockHeld:
  >             raise error.Abort('lockfile on disk even after releasing!')
  >         testlock.release()
  > EOF
  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > testlock=$TESTTMP/testlock.py
  > EOF

  $ hg -R b testlockexc
  abort: expected release exception
  [255]

One process waiting for another

  $ cat > hooks.py << EOF
  > import time
  > def sleepone(**x): time.sleep(1)
  > def sleephalf(**x): time.sleep(0.5)
  > EOF
  $ echo b > b/b
  $ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
  $ hg -R b up -q --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
  > > preup-stdout 2>preup-stderr
  $ wait
  $ cat preup-stdout
  $ cat preup-stderr
  waiting for lock on working directory of b held by process '*' on host '*' (glob)
  got lock after * seconds (glob)
  $ cat stdout
  adding b

On processs waiting on another, warning after a long time.

  $ echo b > b/c
  $ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
  $ hg -R b up -q --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
  > --config ui.timeout.warn=250 \
  > > preup-stdout 2>preup-stderr
  $ wait
  $ cat preup-stdout
  $ cat preup-stderr
  $ cat stdout
  adding c

On processs waiting on another, warning disabled.

  $ echo b > b/d
  $ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
  $ hg -R b up -q --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
  > --config ui.timeout.warn=-1 \
  > > preup-stdout 2>preup-stderr
  $ wait
  $ cat preup-stdout
  $ cat preup-stderr
  $ cat stdout
  adding d

check we still print debug output

On processs waiting on another, warning after a long time (debug output on)

  $ echo b > b/e
  $ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
  $ hg -R b up --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
  > --config ui.timeout.warn=250 --debug\
  > > preup-stdout 2>preup-stderr
  $ wait
  $ cat preup-stdout
  calling hook pre-update: hghook_pre-update.sleephalf
  waiting for lock on working directory of b held by process '*' on host '*' (glob)
  got lock after * seconds (glob)
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat preup-stderr
  $ cat stdout
  adding e

On processs waiting on another, warning disabled, (debug output on)

  $ echo b > b/f
  $ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
  $ hg -R b up --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
  > --config ui.timeout.warn=-1 --debug\
  > > preup-stdout 2>preup-stderr
  $ wait
  $ cat preup-stdout
  calling hook pre-update: hghook_pre-update.sleephalf
  waiting for lock on working directory of b held by process '*' on host '*' (glob)
  got lock after * seconds (glob)
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat preup-stderr
  $ cat stdout
  adding f

Pushing to a local read-only repo that can't be locked

  $ chmod 100 a/.hg/store

  $ hg -R b push a
  pushing to a
  searching for changes
  abort: could not lock repository a: Permission denied
  [255]

  $ chmod 700 a/.hg/store