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sync: reduce multiprocessing serialization overhead

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Background:
 - Manifest object is large (for projects like Android) in terms of
   serialization cost and size (more than 1mb).
 - Lots of Project objects usually share only a few manifest objects.

Before this CL, Project objects were passed to workers via function
parameters. Function parameters are pickled separately (in chunk). In
other words, manifests are serialized again and again. The major
serialization overhead of repo sync was
  O(manifest_size * projects / chunksize)

This CL uses following tricks to reduce serialization overhead.
 - All projects are pickled in one invocation. Because Project objects
   share manifests, pickle library remembers which objects are already
   seen and avoid the serialization cost.
 - Pass the Project objects to workers at worker intialization time.
   And pass project index as function parameters instead. The number of
   workers is much smaller than the number of projects.
 - Worker init state are shared on Linux (fork based). So it requires
   zero serialization for Project objects.

On Linux (fork based), the serialization overhead is
  O(projects)  --- one int per project
On Windows (spawn based), the serialization overhead is
  O(manifest_size * min(workers, projects))

Moreover, use chunksize=1 to avoid the chance that some workers are idle
while other workers still have more than one job in their chunk queue.

Using 2.7k projects as the baseline, originally "repo sync" no-op
sync takes 31s for fetch and 25s for checkout on my Linux workstation.
With this CL, it takes 12s for fetch and 1s for checkout.

Bug: b/371638995
Change-Id: Ifa22072ea54eacb4a5c525c050d84de371e87caa
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/439921
Tested-by: Kuang-che Wu <kcwu@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Kuang-che Wu <kcwu@google.com>
This commit is contained in:
Kuang-che Wu 2024-10-18 23:32:08 +08:00 committed by LUCI
parent 584863fb5e
commit 39ffd9977e
2 changed files with 133 additions and 86 deletions
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50
command.py
View File

@ -12,6 +12,7 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import contextlib
import multiprocessing
import optparse
import os
@ -70,6 +71,14 @@ class Command:
# migrated subcommands can set it to False.
MULTI_MANIFEST_SUPPORT = True
# Shared data across parallel execution workers.
_parallel_context = None
@classmethod
def get_parallel_context(cls):
assert cls._parallel_context is not None
return cls._parallel_context
def __init__(
self,
repodir=None,
@ -242,9 +251,36 @@ class Command:
"""Perform the action, after option parsing is complete."""
raise NotImplementedError
@staticmethod
@classmethod
@contextlib.contextmanager
def ParallelContext(cls):
"""Obtains the context, which is shared to ExecuteInParallel workers.
Callers can store data in the context dict before invocation of
ExecuteInParallel. The dict will then be shared to child workers of
ExecuteInParallel.
"""
assert cls._parallel_context is None
cls._parallel_context = {}
try:
yield
finally:
cls._parallel_context = None
@classmethod
def _SetParallelContext(cls, context):
cls._parallel_context = context
@classmethod
def ExecuteInParallel(
jobs, func, inputs, callback, output=None, ordered=False
cls,
jobs,
func,
inputs,
callback,
output=None,
ordered=False,
chunksize=WORKER_BATCH_SIZE,
):
"""Helper for managing parallel execution boiler plate.
@ -269,6 +305,8 @@ class Command:
output: An output manager. May be progress.Progess or
color.Coloring.
ordered: Whether the jobs should be processed in order.
chunksize: The number of jobs processed in batch by parallel
workers.
Returns:
The |callback| function's results are returned.
@ -278,12 +316,16 @@ class Command:
if len(inputs) == 1 or jobs == 1:
return callback(None, output, (func(x) for x in inputs))
else:
with multiprocessing.Pool(jobs) as pool:
with multiprocessing.Pool(
jobs,
initializer=cls._SetParallelContext,
initargs=(cls._parallel_context,),
) as pool:
submit = pool.imap if ordered else pool.imap_unordered
return callback(
pool,
output,
submit(func, inputs, chunksize=WORKER_BATCH_SIZE),
submit(func, inputs, chunksize=chunksize),
)
finally:
if isinstance(output, progress.Progress):

139
subcmds/sync.py
View File

@ -141,7 +141,7 @@ class _FetchOneResult(NamedTuple):
Attributes:
success (bool): True if successful.
project (Project): The fetched project.
project_idx (int): The fetched project index.
start (float): The starting time.time().
finish (float): The ending time.time().
remote_fetched (bool): True if the remote was actually queried.
@ -149,7 +149,7 @@ class _FetchOneResult(NamedTuple):
success: bool
errors: List[Exception]
project: Project
project_idx: int
start: float
finish: float
remote_fetched: bool
@ -182,14 +182,14 @@ class _CheckoutOneResult(NamedTuple):
Attributes:
success (bool): True if successful.
project (Project): The project.
project_idx (int): The project index.
start (float): The starting time.time().
finish (float): The ending time.time().
"""
success: bool
errors: List[Exception]
project: Project
project_idx: int
start: float
finish: float
@ -592,7 +592,8 @@ later is required to fix a server side protocol bug.
branch = branch[len(R_HEADS) :]
return branch
def _GetCurrentBranchOnly(self, opt, manifest):
@classmethod
def _GetCurrentBranchOnly(cls, opt, manifest):
"""Returns whether current-branch or use-superproject options are
enabled.
@ -710,7 +711,8 @@ later is required to fix a server side protocol bug.
if need_unload:
m.outer_client.manifest.Unload()
def _FetchProjectList(self, opt, projects):
@classmethod
def _FetchProjectList(cls, opt, projects):
"""Main function of the fetch worker.
The projects we're given share the same underlying git object store, so
@ -722,21 +724,23 @@ later is required to fix a server side protocol bug.
opt: Program options returned from optparse. See _Options().
projects: Projects to fetch.
"""
return [self._FetchOne(opt, x) for x in projects]
return [cls._FetchOne(opt, x) for x in projects]
def _FetchOne(self, opt, project):
@classmethod
def _FetchOne(cls, opt, project_idx):
"""Fetch git objects for a single project.
Args:
opt: Program options returned from optparse. See _Options().
project: Project object for the project to fetch.
project_idx: Project index for the project to fetch.
Returns:
Whether the fetch was successful.
"""
project = cls.get_parallel_context()["projects"][project_idx]
start = time.time()
k = f"{project.name} @ {project.relpath}"
self._sync_dict[k] = start
cls.get_parallel_context()["sync_dict"][k] = start
success = False
remote_fetched = False
errors = []
@ -746,7 +750,7 @@ later is required to fix a server side protocol bug.
quiet=opt.quiet,
verbose=opt.verbose,
output_redir=buf,
current_branch_only=self._GetCurrentBranchOnly(
current_branch_only=cls._GetCurrentBranchOnly(
opt, project.manifest
),
force_sync=opt.force_sync,
@ -756,7 +760,7 @@ later is required to fix a server side protocol bug.
optimized_fetch=opt.optimized_fetch,
retry_fetches=opt.retry_fetches,
prune=opt.prune,
ssh_proxy=self.ssh_proxy,
ssh_proxy=cls.get_parallel_context()["ssh_proxy"],
clone_filter=project.manifest.CloneFilter,
partial_clone_exclude=project.manifest.PartialCloneExclude,
clone_filter_for_depth=project.manifest.CloneFilterForDepth,
@ -788,24 +792,20 @@ later is required to fix a server side protocol bug.
type(e).__name__,
e,
)
del self._sync_dict[k]
errors.append(e)
raise
finally:
del cls.get_parallel_context()["sync_dict"][k]
finish = time.time()
del self._sync_dict[k]
return _FetchOneResult(
success, errors, project, start, finish, remote_fetched
success, errors, project_idx, start, finish, remote_fetched
)
@classmethod
def _FetchInitChild(cls, ssh_proxy):
cls.ssh_proxy = ssh_proxy
def _GetSyncProgressMessage(self):
earliest_time = float("inf")
earliest_proj = None
items = self._sync_dict.items()
items = self.get_parallel_context()["sync_dict"].items()
for project, t in items:
if t < earliest_time:
earliest_time = t
@ -813,7 +813,7 @@ later is required to fix a server side protocol bug.
if not earliest_proj:
# This function is called when sync is still running but in some
# cases (by chance), _sync_dict can contain no entries. Return some
# cases (by chance), sync_dict can contain no entries. Return some
# text to indicate that sync is still working.
return "..working.."
@ -835,7 +835,6 @@ later is required to fix a server side protocol bug.
elide=True,
)
self._sync_dict = multiprocessing.Manager().dict()
sync_event = _threading.Event()
def _MonitorSyncLoop():
@ -846,21 +845,13 @@ later is required to fix a server side protocol bug.
sync_progress_thread = _threading.Thread(target=_MonitorSyncLoop)
sync_progress_thread.daemon = True
sync_progress_thread.start()
objdir_project_map = dict()
for project in projects:
objdir_project_map.setdefault(project.objdir, []).append(project)
projects_list = list(objdir_project_map.values())
jobs = min(opt.jobs_network, len(projects_list))
def _ProcessResults(results_sets):
def _ProcessResults(pool, pm, results_sets):
ret = True
for results in results_sets:
for result in results:
success = result.success
project = result.project
project = projects[result.project_idx]
start = result.start
finish = result.finish
self._fetch_times.Set(project, finish - start)
@ -884,45 +875,49 @@ later is required to fix a server side protocol bug.
fetched.add(project.gitdir)
pm.update()
if not ret and opt.fail_fast:
if pool:
pool.close()
break
return ret
# We pass the ssh proxy settings via the class. This allows
# multiprocessing to pickle it up when spawning children. We can't pass
# it as an argument to _FetchProjectList below as multiprocessing is
# unable to pickle those.
Sync.ssh_proxy = None
with self.ParallelContext():
self.get_parallel_context()["projects"] = projects
self.get_parallel_context()[
"sync_dict"
] = multiprocessing.Manager().dict()
# NB: Multiprocessing is heavy, so don't spin it up for one job.
if jobs == 1:
self._FetchInitChild(ssh_proxy)
if not _ProcessResults(
self._FetchProjectList(opt, x) for x in projects_list
):
ret = False
else:
objdir_project_map = dict()
for index, project in enumerate(projects):
objdir_project_map.setdefault(project.objdir, []).append(index)
projects_list = list(objdir_project_map.values())
jobs = min(opt.jobs_network, len(projects_list))
# We pass the ssh proxy settings via the class. This allows
# multiprocessing to pickle it up when spawning children. We can't
# pass it as an argument to _FetchProjectList below as
# multiprocessing is unable to pickle those.
self.get_parallel_context()["ssh_proxy"] = ssh_proxy
sync_progress_thread.start()
if not opt.quiet:
pm.update(inc=0, msg="warming up")
with multiprocessing.Pool(
jobs, initializer=self._FetchInitChild, initargs=(ssh_proxy,)
) as pool:
results = pool.imap_unordered(
try:
ret = self.ExecuteInParallel(
jobs,
functools.partial(self._FetchProjectList, opt),
projects_list,
chunksize=_chunksize(len(projects_list), jobs),
callback=_ProcessResults,
output=pm,
# Use chunksize=1 to avoid the chance that some workers are
# idle while other workers still have more than one job in
# their chunk queue.
chunksize=1,
)
if not _ProcessResults(results):
ret = False
pool.close()
# Cleanup the reference now that we're done with it, and we're going to
# release any resources it points to. If we don't, later
# multiprocessing usage (e.g. checkouts) will try to pickle and then
# crash.
del Sync.ssh_proxy
finally:
sync_event.set()
pm.end()
sync_progress_thread.join()
self._fetch_times.Save()
self._local_sync_state.Save()
@ -1008,14 +1003,15 @@ later is required to fix a server side protocol bug.
return _FetchMainResult(all_projects)
@classmethod
def _CheckoutOne(
self,
cls,
detach_head,
force_sync,
force_checkout,
force_rebase,
verbose,
project,
project_idx,
):
"""Checkout work tree for one project
@ -1027,11 +1023,12 @@ later is required to fix a server side protocol bug.
force_checkout: Force checking out of the repo content.
force_rebase: Force rebase.
verbose: Whether to show verbose messages.
project: Project object for the project to checkout.
project_idx: Project index for the project to checkout.
Returns:
Whether the fetch was successful.
"""
project = cls.get_parallel_context()["projects"][project_idx]
start = time.time()
syncbuf = SyncBuffer(
project.manifest.manifestProject.config, detach_head=detach_head
@ -1065,7 +1062,7 @@ later is required to fix a server side protocol bug.
if not success:
logger.error("error: Cannot checkout %s", project.name)
finish = time.time()
return _CheckoutOneResult(success, errors, project, start, finish)
return _CheckoutOneResult(success, errors, project_idx, start, finish)
def _Checkout(self, all_projects, opt, err_results, checkout_errors):
"""Checkout projects listed in all_projects
@ -1083,7 +1080,9 @@ later is required to fix a server side protocol bug.
ret = True
for result in results:
success = result.success
project = result.project
project = self.get_parallel_context()["projects"][
result.project_idx
]
start = result.start
finish = result.finish
self.event_log.AddSync(
@ -1110,6 +1109,8 @@ later is required to fix a server side protocol bug.
return ret
for projects in _SafeCheckoutOrder(all_projects):
with self.ParallelContext():
self.get_parallel_context()["projects"] = projects
proc_res = self.ExecuteInParallel(
opt.jobs_checkout,
functools.partial(
@ -1120,11 +1121,15 @@ later is required to fix a server side protocol bug.
opt.rebase,
opt.verbose,
),
projects,
range(len(projects)),
callback=_ProcessResults,
output=Progress(
"Checking out", len(all_projects), quiet=opt.quiet
),
# Use chunksize=1 to avoid the chance that some workers are
# idle while other workers still have more than one job in
# their chunk queue.
chunksize=1,
)
self._local_sync_state.Save()