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@@ -1,325 +1,327 b'' | |||||
1 | # worker.py - master-slave parallelism support |
|
1 | # worker.py - master-slave parallelism support | |
2 | # |
|
2 | # | |
3 | # Copyright 2013 Facebook, Inc. |
|
3 | # Copyright 2013 Facebook, Inc. | |
4 | # |
|
4 | # | |
5 | # This software may be used and distributed according to the terms of the |
|
5 | # This software may be used and distributed according to the terms of the | |
6 | # GNU General Public License version 2 or any later version. |
|
6 | # GNU General Public License version 2 or any later version. | |
7 |
|
7 | |||
8 | from __future__ import absolute_import |
|
8 | from __future__ import absolute_import | |
9 |
|
9 | |||
10 | import errno |
|
10 | import errno | |
11 | import os |
|
11 | import os | |
12 | import signal |
|
12 | import signal | |
13 | import sys |
|
13 | import sys | |
14 | import threading |
|
14 | import threading | |
|
15 | import time | |||
15 |
|
16 | |||
16 | from .i18n import _ |
|
17 | from .i18n import _ | |
17 | from . import ( |
|
18 | from . import ( | |
18 | encoding, |
|
19 | encoding, | |
19 | error, |
|
20 | error, | |
20 | pycompat, |
|
21 | pycompat, | |
21 | scmutil, |
|
22 | scmutil, | |
22 | util, |
|
23 | util, | |
23 | ) |
|
24 | ) | |
24 |
|
25 | |||
25 | def countcpus(): |
|
26 | def countcpus(): | |
26 | '''try to count the number of CPUs on the system''' |
|
27 | '''try to count the number of CPUs on the system''' | |
27 |
|
28 | |||
28 | # posix |
|
29 | # posix | |
29 | try: |
|
30 | try: | |
30 | n = int(os.sysconf(r'SC_NPROCESSORS_ONLN')) |
|
31 | n = int(os.sysconf(r'SC_NPROCESSORS_ONLN')) | |
31 | if n > 0: |
|
32 | if n > 0: | |
32 | return n |
|
33 | return n | |
33 | except (AttributeError, ValueError): |
|
34 | except (AttributeError, ValueError): | |
34 | pass |
|
35 | pass | |
35 |
|
36 | |||
36 | # windows |
|
37 | # windows | |
37 | try: |
|
38 | try: | |
38 | n = int(encoding.environ['NUMBER_OF_PROCESSORS']) |
|
39 | n = int(encoding.environ['NUMBER_OF_PROCESSORS']) | |
39 | if n > 0: |
|
40 | if n > 0: | |
40 | return n |
|
41 | return n | |
41 | except (KeyError, ValueError): |
|
42 | except (KeyError, ValueError): | |
42 | pass |
|
43 | pass | |
43 |
|
44 | |||
44 | return 1 |
|
45 | return 1 | |
45 |
|
46 | |||
46 | def _numworkers(ui): |
|
47 | def _numworkers(ui): | |
47 | s = ui.config('worker', 'numcpus') |
|
48 | s = ui.config('worker', 'numcpus') | |
48 | if s: |
|
49 | if s: | |
49 | try: |
|
50 | try: | |
50 | n = int(s) |
|
51 | n = int(s) | |
51 | if n >= 1: |
|
52 | if n >= 1: | |
52 | return n |
|
53 | return n | |
53 | except ValueError: |
|
54 | except ValueError: | |
54 | raise error.Abort(_('number of cpus must be an integer')) |
|
55 | raise error.Abort(_('number of cpus must be an integer')) | |
55 | return min(max(countcpus(), 4), 32) |
|
56 | return min(max(countcpus(), 4), 32) | |
56 |
|
57 | |||
57 | if pycompat.isposix or pycompat.iswindows: |
|
58 | if pycompat.isposix or pycompat.iswindows: | |
58 | _startupcost = 0.01 |
|
59 | _startupcost = 0.01 | |
59 | else: |
|
60 | else: | |
60 | _startupcost = 1e30 |
|
61 | _startupcost = 1e30 | |
61 |
|
62 | |||
62 | def worthwhile(ui, costperop, nops): |
|
63 | def worthwhile(ui, costperop, nops): | |
63 | '''try to determine whether the benefit of multiple processes can |
|
64 | '''try to determine whether the benefit of multiple processes can | |
64 | outweigh the cost of starting them''' |
|
65 | outweigh the cost of starting them''' | |
65 | linear = costperop * nops |
|
66 | linear = costperop * nops | |
66 | workers = _numworkers(ui) |
|
67 | workers = _numworkers(ui) | |
67 | benefit = linear - (_startupcost * workers + linear / workers) |
|
68 | benefit = linear - (_startupcost * workers + linear / workers) | |
68 | return benefit >= 0.15 |
|
69 | return benefit >= 0.15 | |
69 |
|
70 | |||
70 | def worker(ui, costperarg, func, staticargs, args): |
|
71 | def worker(ui, costperarg, func, staticargs, args): | |
71 | '''run a function, possibly in parallel in multiple worker |
|
72 | '''run a function, possibly in parallel in multiple worker | |
72 | processes. |
|
73 | processes. | |
73 |
|
74 | |||
74 | returns a progress iterator |
|
75 | returns a progress iterator | |
75 |
|
76 | |||
76 | costperarg - cost of a single task |
|
77 | costperarg - cost of a single task | |
77 |
|
78 | |||
78 | func - function to run |
|
79 | func - function to run | |
79 |
|
80 | |||
80 | staticargs - arguments to pass to every invocation of the function |
|
81 | staticargs - arguments to pass to every invocation of the function | |
81 |
|
82 | |||
82 | args - arguments to split into chunks, to pass to individual |
|
83 | args - arguments to split into chunks, to pass to individual | |
83 | workers |
|
84 | workers | |
84 | ''' |
|
85 | ''' | |
85 | enabled = ui.configbool('worker', 'enabled') |
|
86 | enabled = ui.configbool('worker', 'enabled') | |
86 | if enabled and worthwhile(ui, costperarg, len(args)): |
|
87 | if enabled and worthwhile(ui, costperarg, len(args)): | |
87 | return _platformworker(ui, func, staticargs, args) |
|
88 | return _platformworker(ui, func, staticargs, args) | |
88 | return func(*staticargs + (args,)) |
|
89 | return func(*staticargs + (args,)) | |
89 |
|
90 | |||
90 | def _posixworker(ui, func, staticargs, args): |
|
91 | def _posixworker(ui, func, staticargs, args): | |
91 | rfd, wfd = os.pipe() |
|
92 | rfd, wfd = os.pipe() | |
92 | workers = _numworkers(ui) |
|
93 | workers = _numworkers(ui) | |
93 | oldhandler = signal.getsignal(signal.SIGINT) |
|
94 | oldhandler = signal.getsignal(signal.SIGINT) | |
94 | signal.signal(signal.SIGINT, signal.SIG_IGN) |
|
95 | signal.signal(signal.SIGINT, signal.SIG_IGN) | |
95 | pids, problem = set(), [0] |
|
96 | pids, problem = set(), [0] | |
96 | def killworkers(): |
|
97 | def killworkers(): | |
97 | # unregister SIGCHLD handler as all children will be killed. This |
|
98 | # unregister SIGCHLD handler as all children will be killed. This | |
98 | # function shouldn't be interrupted by another SIGCHLD; otherwise pids |
|
99 | # function shouldn't be interrupted by another SIGCHLD; otherwise pids | |
99 | # could be updated while iterating, which would cause inconsistency. |
|
100 | # could be updated while iterating, which would cause inconsistency. | |
100 | signal.signal(signal.SIGCHLD, oldchldhandler) |
|
101 | signal.signal(signal.SIGCHLD, oldchldhandler) | |
101 | # if one worker bails, there's no good reason to wait for the rest |
|
102 | # if one worker bails, there's no good reason to wait for the rest | |
102 | for p in pids: |
|
103 | for p in pids: | |
103 | try: |
|
104 | try: | |
104 | os.kill(p, signal.SIGTERM) |
|
105 | os.kill(p, signal.SIGTERM) | |
105 | except OSError as err: |
|
106 | except OSError as err: | |
106 | if err.errno != errno.ESRCH: |
|
107 | if err.errno != errno.ESRCH: | |
107 | raise |
|
108 | raise | |
108 | def waitforworkers(blocking=True): |
|
109 | def waitforworkers(blocking=True): | |
109 | for pid in pids.copy(): |
|
110 | for pid in pids.copy(): | |
110 | p = st = 0 |
|
111 | p = st = 0 | |
111 | while True: |
|
112 | while True: | |
112 | try: |
|
113 | try: | |
113 | p, st = os.waitpid(pid, (0 if blocking else os.WNOHANG)) |
|
114 | p, st = os.waitpid(pid, (0 if blocking else os.WNOHANG)) | |
114 | break |
|
115 | break | |
115 | except OSError as e: |
|
116 | except OSError as e: | |
116 | if e.errno == errno.EINTR: |
|
117 | if e.errno == errno.EINTR: | |
117 | continue |
|
118 | continue | |
118 | elif e.errno == errno.ECHILD: |
|
119 | elif e.errno == errno.ECHILD: | |
119 | # child would already be reaped, but pids yet been |
|
120 | # child would already be reaped, but pids yet been | |
120 | # updated (maybe interrupted just after waitpid) |
|
121 | # updated (maybe interrupted just after waitpid) | |
121 | pids.discard(pid) |
|
122 | pids.discard(pid) | |
122 | break |
|
123 | break | |
123 | else: |
|
124 | else: | |
124 | raise |
|
125 | raise | |
125 | if not p: |
|
126 | if not p: | |
126 | # skip subsequent steps, because child process should |
|
127 | # skip subsequent steps, because child process should | |
127 | # be still running in this case |
|
128 | # be still running in this case | |
128 | continue |
|
129 | continue | |
129 | pids.discard(p) |
|
130 | pids.discard(p) | |
130 | st = _exitstatus(st) |
|
131 | st = _exitstatus(st) | |
131 | if st and not problem[0]: |
|
132 | if st and not problem[0]: | |
132 | problem[0] = st |
|
133 | problem[0] = st | |
133 | def sigchldhandler(signum, frame): |
|
134 | def sigchldhandler(signum, frame): | |
134 | waitforworkers(blocking=False) |
|
135 | waitforworkers(blocking=False) | |
135 | if problem[0]: |
|
136 | if problem[0]: | |
136 | killworkers() |
|
137 | killworkers() | |
137 | oldchldhandler = signal.signal(signal.SIGCHLD, sigchldhandler) |
|
138 | oldchldhandler = signal.signal(signal.SIGCHLD, sigchldhandler) | |
138 | ui.flush() |
|
139 | ui.flush() | |
139 | parentpid = os.getpid() |
|
140 | parentpid = os.getpid() | |
140 | for pargs in partition(args, workers): |
|
141 | for pargs in partition(args, workers): | |
141 | # make sure we use os._exit in all worker code paths. otherwise the |
|
142 | # make sure we use os._exit in all worker code paths. otherwise the | |
142 | # worker may do some clean-ups which could cause surprises like |
|
143 | # worker may do some clean-ups which could cause surprises like | |
143 | # deadlock. see sshpeer.cleanup for example. |
|
144 | # deadlock. see sshpeer.cleanup for example. | |
144 | # override error handling *before* fork. this is necessary because |
|
145 | # override error handling *before* fork. this is necessary because | |
145 | # exception (signal) may arrive after fork, before "pid =" assignment |
|
146 | # exception (signal) may arrive after fork, before "pid =" assignment | |
146 | # completes, and other exception handler (dispatch.py) can lead to |
|
147 | # completes, and other exception handler (dispatch.py) can lead to | |
147 | # unexpected code path without os._exit. |
|
148 | # unexpected code path without os._exit. | |
148 | ret = -1 |
|
149 | ret = -1 | |
149 | try: |
|
150 | try: | |
150 | pid = os.fork() |
|
151 | pid = os.fork() | |
151 | if pid == 0: |
|
152 | if pid == 0: | |
152 | signal.signal(signal.SIGINT, oldhandler) |
|
153 | signal.signal(signal.SIGINT, oldhandler) | |
153 | signal.signal(signal.SIGCHLD, oldchldhandler) |
|
154 | signal.signal(signal.SIGCHLD, oldchldhandler) | |
154 |
|
155 | |||
155 | def workerfunc(): |
|
156 | def workerfunc(): | |
156 | os.close(rfd) |
|
157 | os.close(rfd) | |
157 | for i, item in func(*(staticargs + (pargs,))): |
|
158 | for i, item in func(*(staticargs + (pargs,))): | |
158 | os.write(wfd, '%d %s\n' % (i, item)) |
|
159 | os.write(wfd, '%d %s\n' % (i, item)) | |
159 | return 0 |
|
160 | return 0 | |
160 |
|
161 | |||
161 | ret = scmutil.callcatch(ui, workerfunc) |
|
162 | ret = scmutil.callcatch(ui, workerfunc) | |
162 | except: # parent re-raises, child never returns |
|
163 | except: # parent re-raises, child never returns | |
163 | if os.getpid() == parentpid: |
|
164 | if os.getpid() == parentpid: | |
164 | raise |
|
165 | raise | |
165 | exctype = sys.exc_info()[0] |
|
166 | exctype = sys.exc_info()[0] | |
166 | force = not issubclass(exctype, KeyboardInterrupt) |
|
167 | force = not issubclass(exctype, KeyboardInterrupt) | |
167 | ui.traceback(force=force) |
|
168 | ui.traceback(force=force) | |
168 | finally: |
|
169 | finally: | |
169 | if os.getpid() != parentpid: |
|
170 | if os.getpid() != parentpid: | |
170 | try: |
|
171 | try: | |
171 | ui.flush() |
|
172 | ui.flush() | |
172 | except: # never returns, no re-raises |
|
173 | except: # never returns, no re-raises | |
173 | pass |
|
174 | pass | |
174 | finally: |
|
175 | finally: | |
175 | os._exit(ret & 255) |
|
176 | os._exit(ret & 255) | |
176 | pids.add(pid) |
|
177 | pids.add(pid) | |
177 | os.close(wfd) |
|
178 | os.close(wfd) | |
178 | fp = os.fdopen(rfd, pycompat.sysstr('rb'), 0) |
|
179 | fp = os.fdopen(rfd, pycompat.sysstr('rb'), 0) | |
179 | def cleanup(): |
|
180 | def cleanup(): | |
180 | signal.signal(signal.SIGINT, oldhandler) |
|
181 | signal.signal(signal.SIGINT, oldhandler) | |
181 | waitforworkers() |
|
182 | waitforworkers() | |
182 | signal.signal(signal.SIGCHLD, oldchldhandler) |
|
183 | signal.signal(signal.SIGCHLD, oldchldhandler) | |
183 | status = problem[0] |
|
184 | status = problem[0] | |
184 | if status: |
|
185 | if status: | |
185 | if status < 0: |
|
186 | if status < 0: | |
186 | os.kill(os.getpid(), -status) |
|
187 | os.kill(os.getpid(), -status) | |
187 | sys.exit(status) |
|
188 | sys.exit(status) | |
188 | try: |
|
189 | try: | |
189 | for line in util.iterfile(fp): |
|
190 | for line in util.iterfile(fp): | |
190 | l = line.split(' ', 1) |
|
191 | l = line.split(' ', 1) | |
191 | yield int(l[0]), l[1][:-1] |
|
192 | yield int(l[0]), l[1][:-1] | |
192 | except: # re-raises |
|
193 | except: # re-raises | |
193 | killworkers() |
|
194 | killworkers() | |
194 | cleanup() |
|
195 | cleanup() | |
195 | raise |
|
196 | raise | |
196 | cleanup() |
|
197 | cleanup() | |
197 |
|
198 | |||
198 | def _posixexitstatus(code): |
|
199 | def _posixexitstatus(code): | |
199 | '''convert a posix exit status into the same form returned by |
|
200 | '''convert a posix exit status into the same form returned by | |
200 | os.spawnv |
|
201 | os.spawnv | |
201 |
|
202 | |||
202 | returns None if the process was stopped instead of exiting''' |
|
203 | returns None if the process was stopped instead of exiting''' | |
203 | if os.WIFEXITED(code): |
|
204 | if os.WIFEXITED(code): | |
204 | return os.WEXITSTATUS(code) |
|
205 | return os.WEXITSTATUS(code) | |
205 | elif os.WIFSIGNALED(code): |
|
206 | elif os.WIFSIGNALED(code): | |
206 | return -os.WTERMSIG(code) |
|
207 | return -os.WTERMSIG(code) | |
207 |
|
208 | |||
208 | def _windowsworker(ui, func, staticargs, args): |
|
209 | def _windowsworker(ui, func, staticargs, args): | |
209 | class Worker(threading.Thread): |
|
210 | class Worker(threading.Thread): | |
210 | def __init__(self, taskqueue, resultqueue, func, staticargs, |
|
211 | def __init__(self, taskqueue, resultqueue, func, staticargs, | |
211 | group=None, target=None, name=None, verbose=None): |
|
212 | group=None, target=None, name=None, verbose=None): | |
212 | threading.Thread.__init__(self, group=group, target=target, |
|
213 | threading.Thread.__init__(self, group=group, target=target, | |
213 | name=name, verbose=verbose) |
|
214 | name=name, verbose=verbose) | |
214 | self._taskqueue = taskqueue |
|
215 | self._taskqueue = taskqueue | |
215 | self._resultqueue = resultqueue |
|
216 | self._resultqueue = resultqueue | |
216 | self._func = func |
|
217 | self._func = func | |
217 | self._staticargs = staticargs |
|
218 | self._staticargs = staticargs | |
218 | self._interrupted = False |
|
219 | self._interrupted = False | |
|
220 | self.daemon = True | |||
219 | self.exception = None |
|
221 | self.exception = None | |
220 |
|
222 | |||
221 | def interrupt(self): |
|
223 | def interrupt(self): | |
222 | self._interrupted = True |
|
224 | self._interrupted = True | |
223 |
|
225 | |||
224 | def run(self): |
|
226 | def run(self): | |
225 | try: |
|
227 | try: | |
226 | while not self._taskqueue.empty(): |
|
228 | while not self._taskqueue.empty(): | |
227 | try: |
|
229 | try: | |
228 | args = self._taskqueue.get_nowait() |
|
230 | args = self._taskqueue.get_nowait() | |
229 | for res in self._func(*self._staticargs + (args,)): |
|
231 | for res in self._func(*self._staticargs + (args,)): | |
230 | self._resultqueue.put(res) |
|
232 | self._resultqueue.put(res) | |
231 | # threading doesn't provide a native way to |
|
233 | # threading doesn't provide a native way to | |
232 | # interrupt execution. handle it manually at every |
|
234 | # interrupt execution. handle it manually at every | |
233 | # iteration. |
|
235 | # iteration. | |
234 | if self._interrupted: |
|
236 | if self._interrupted: | |
235 | return |
|
237 | return | |
236 | except util.empty: |
|
238 | except util.empty: | |
237 | break |
|
239 | break | |
238 | except Exception as e: |
|
240 | except Exception as e: | |
239 | # store the exception such that the main thread can resurface |
|
241 | # store the exception such that the main thread can resurface | |
240 | # it as if the func was running without workers. |
|
242 | # it as if the func was running without workers. | |
241 | self.exception = e |
|
243 | self.exception = e | |
242 | raise |
|
244 | raise | |
243 |
|
245 | |||
244 | threads = [] |
|
246 | threads = [] | |
245 | def killworkers(): |
|
247 | def trykillworkers(): | |
|
248 | # Allow up to 1 second to clean worker threads nicely | |||
|
249 | cleanupend = time.time() + 1 | |||
246 | for t in threads: |
|
250 | for t in threads: | |
247 | t.interrupt() |
|
251 | t.interrupt() | |
248 | for t in threads: |
|
252 | for t in threads: | |
249 | # try to let the threads handle interruption, but don't wait |
|
253 | remainingtime = cleanupend - time.time() | |
250 | # indefintely. the thread could be in infinite loop, handling |
|
254 | t.join(remainingtime) | |
251 | # a very long task or in a deadlock situation |
|
|||
252 | t.join(5) |
|
|||
253 | if t.is_alive(): |
|
255 | if t.is_alive(): | |
254 | raise error.Abort(_('failed to join worker thread')) |
|
256 | # pass over the workers joining failure. it is more | |
|
257 | # important to surface the inital exception than the | |||
|
258 | # fact that one of workers may be processing a large | |||
|
259 | # task and does not get to handle the interruption. | |||
|
260 | ui.warn(_("failed to kill worker threads while " | |||
|
261 | "handling an exception\n")) | |||
|
262 | return | |||
255 |
|
263 | |||
256 | workers = _numworkers(ui) |
|
264 | workers = _numworkers(ui) | |
257 | resultqueue = util.queue() |
|
265 | resultqueue = util.queue() | |
258 | taskqueue = util.queue() |
|
266 | taskqueue = util.queue() | |
259 | # partition work to more pieces than workers to minimize the chance |
|
267 | # partition work to more pieces than workers to minimize the chance | |
260 | # of uneven distribution of large tasks between the workers |
|
268 | # of uneven distribution of large tasks between the workers | |
261 | for pargs in partition(args, workers * 20): |
|
269 | for pargs in partition(args, workers * 20): | |
262 | taskqueue.put(pargs) |
|
270 | taskqueue.put(pargs) | |
263 | for _i in range(workers): |
|
271 | for _i in range(workers): | |
264 | t = Worker(taskqueue, resultqueue, func, staticargs) |
|
272 | t = Worker(taskqueue, resultqueue, func, staticargs) | |
265 | threads.append(t) |
|
273 | threads.append(t) | |
266 | t.start() |
|
274 | t.start() | |
267 |
|
275 | try: | ||
268 | while len(threads) > 0: |
|
276 | while len(threads) > 0: | |
269 | while not resultqueue.empty(): |
|
277 | while not resultqueue.empty(): | |
270 | yield resultqueue.get() |
|
278 | yield resultqueue.get() | |
271 | threads[0].join(0.05) |
|
279 | threads[0].join(0.05) | |
272 | finishedthreads = [_t for _t in threads if not _t.is_alive()] |
|
280 | finishedthreads = [_t for _t in threads if not _t.is_alive()] | |
273 | for t in finishedthreads: |
|
281 | for t in finishedthreads: | |
274 | if t.exception is not None: |
|
282 | if t.exception is not None: | |
275 | try: |
|
283 | raise t.exception | |
276 |
|
|
284 | threads.remove(t) | |
277 |
|
|
285 | except Exception: # re-raises | |
278 | # pass over the workers joining failure. it is more |
|
286 | trykillworkers() | |
279 | # important to surface the inital exception than the |
|
287 | raise | |
280 | # fact that one of workers may be processing a large |
|
|||
281 | # task and does not get to handle the interruption. |
|
|||
282 | ui.warn(_("failed to kill worker threads while handling " |
|
|||
283 | "an exception")) |
|
|||
284 | raise t.exception |
|
|||
285 | threads.remove(t) |
|
|||
286 | while not resultqueue.empty(): |
|
288 | while not resultqueue.empty(): | |
287 | yield resultqueue.get() |
|
289 | yield resultqueue.get() | |
288 |
|
290 | |||
289 | if pycompat.iswindows: |
|
291 | if pycompat.iswindows: | |
290 | _platformworker = _windowsworker |
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292 | _platformworker = _windowsworker | |
291 | else: |
|
293 | else: | |
292 | _platformworker = _posixworker |
|
294 | _platformworker = _posixworker | |
293 | _exitstatus = _posixexitstatus |
|
295 | _exitstatus = _posixexitstatus | |
294 |
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296 | |||
295 | def partition(lst, nslices): |
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297 | def partition(lst, nslices): | |
296 | '''partition a list into N slices of roughly equal size |
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298 | '''partition a list into N slices of roughly equal size | |
297 |
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299 | |||
298 | The current strategy takes every Nth element from the input. If |
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300 | The current strategy takes every Nth element from the input. If | |
299 | we ever write workers that need to preserve grouping in input |
|
301 | we ever write workers that need to preserve grouping in input | |
300 | we should consider allowing callers to specify a partition strategy. |
|
302 | we should consider allowing callers to specify a partition strategy. | |
301 |
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303 | |||
302 | mpm is not a fan of this partitioning strategy when files are involved. |
|
304 | mpm is not a fan of this partitioning strategy when files are involved. | |
303 | In his words: |
|
305 | In his words: | |
304 |
|
306 | |||
305 | Single-threaded Mercurial makes a point of creating and visiting |
|
307 | Single-threaded Mercurial makes a point of creating and visiting | |
306 | files in a fixed order (alphabetical). When creating files in order, |
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308 | files in a fixed order (alphabetical). When creating files in order, | |
307 | a typical filesystem is likely to allocate them on nearby regions on |
|
309 | a typical filesystem is likely to allocate them on nearby regions on | |
308 | disk. Thus, when revisiting in the same order, locality is maximized |
|
310 | disk. Thus, when revisiting in the same order, locality is maximized | |
309 | and various forms of OS and disk-level caching and read-ahead get a |
|
311 | and various forms of OS and disk-level caching and read-ahead get a | |
310 | chance to work. |
|
312 | chance to work. | |
311 |
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313 | |||
312 | This effect can be quite significant on spinning disks. I discovered it |
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314 | This effect can be quite significant on spinning disks. I discovered it | |
313 | circa Mercurial v0.4 when revlogs were named by hashes of filenames. |
|
315 | circa Mercurial v0.4 when revlogs were named by hashes of filenames. | |
314 | Tarring a repo and copying it to another disk effectively randomized |
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316 | Tarring a repo and copying it to another disk effectively randomized | |
315 | the revlog ordering on disk by sorting the revlogs by hash and suddenly |
|
317 | the revlog ordering on disk by sorting the revlogs by hash and suddenly | |
316 | performance of my kernel checkout benchmark dropped by ~10x because the |
|
318 | performance of my kernel checkout benchmark dropped by ~10x because the | |
317 | "working set" of sectors visited no longer fit in the drive's cache and |
|
319 | "working set" of sectors visited no longer fit in the drive's cache and | |
318 | the workload switched from streaming to random I/O. |
|
320 | the workload switched from streaming to random I/O. | |
319 |
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321 | |||
320 | What we should really be doing is have workers read filenames from a |
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322 | What we should really be doing is have workers read filenames from a | |
321 | ordered queue. This preserves locality and also keeps any worker from |
|
323 | ordered queue. This preserves locality and also keeps any worker from | |
322 | getting more than one file out of balance. |
|
324 | getting more than one file out of balance. | |
323 | ''' |
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325 | ''' | |
324 | for i in range(nslices): |
|
326 | for i in range(nslices): | |
325 | yield lst[i::nslices] |
|
327 | yield lst[i::nslices] |
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