worker: estimate whether it's worth running a task in parallel
Not implemented for Windows yet.
--- a/mercurial/help/config.txt Sat Feb 09 15:22:12 2013 -0800
+++ b/mercurial/help/config.txt Sat Feb 09 15:51:26 2013 -0800
@@ -1463,3 +1463,15 @@
``templates``
Where to find the HTML templates. Default is install path.
+
+``worker``
+----------
+
+Parallel master/worker configuration. We currently perform working
+directory updates in parallel on Unix-like systems, which greatly
+helps performance.
+
+``numcpus``
+ Number of CPUs to use for parallel operations. Default is 4 or the
+ number of CPUs on the system, whichever is larger. A zero or
+ negative value is treated as ``use the default``.
--- a/mercurial/worker.py Sat Feb 09 15:22:12 2013 -0800
+++ b/mercurial/worker.py Sat Feb 09 15:51:26 2013 -0800
@@ -5,7 +5,8 @@
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
-import os
+from i18n import _
+import os, util
def countcpus():
'''try to count the number of CPUs on the system'''
@@ -27,3 +28,27 @@
pass
return 1
+
+def _numworkers(ui):
+ s = ui.config('worker', 'numcpus')
+ if s:
+ try:
+ n = int(s)
+ if n >= 1:
+ return n
+ except ValueError:
+ raise util.Abort(_('number of cpus must be an integer'))
+ return min(max(countcpus(), 4), 32)
+
+if os.name == 'posix':
+ _startupcost = 0.01
+else:
+ _startupcost = 1e30
+
+def worthwhile(ui, costperop, nops):
+ '''try to determine whether the benefit of multiple processes can
+ outweigh the cost of starting them'''
+ linear = costperop * nops
+ workers = _numworkers(ui)
+ benefit = linear - (_startupcost * workers + linear / workers)
+ return benefit >= 0.15