Enable merging buildbot builds dependent on queue length

masters/master.client.v8/master.cfg

 # -*- python -*-
 # ex: set syntax=python:
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+
+from buildbot.process import buildrequest
 from buildbot.scheduler import Nightly
 from buildbot.scheduler import Scheduler
 
 from master import gitiles_poller
 from master import master_config
 from master import master_utils
 from master import slaves_list
 from master.factory import annotator_factory
 
 import config
 import master_site_config
 
+import math
 import os
 
 
 ActiveMaster = master_site_config.V8
 MAIL_NOTIFIER = ActiveMaster.is_production_host
 
 # This is the dictionary that the buildmaster pays attention to. We also use
 # a shorter alias to save typing.
 c = BuildmasterConfig = {}
 c['status'] = []
 
+def merge_requests_logarithmic(req1, req2, queue_length=1):
+  """Merges builds dependent on the number of builds in the queue."""
+  if not buildrequest.BuildRequest.canBeMergedWith(req1, req2):
+    return False
+
+  # We inject our own data into the left build request's dict to keep track of
+  # the number of merged builds. Buildbot compares the left one with all others
+  # in the queue.
+  num = req1.brdict.setdefault('monkey_patch_merged', 2)
+  if num > int(math.log(queue_length or 1, 2)) + 1:
+    return False
+  req1.brdict['monkey_patch_merged'] = num + 1
+  return True
 
 ####### DATABASE
 
 config.DatabaseSetup(c)
 
 ####### CHANGESOURCES
 
 comparator = gitiles_poller.GitilesRevisionComparator()
 c['change_source'] = [
   gitiles_poller.GitilesPoller(
@@ skipping 177 matching lines @@
   'factory': m_annotator.BaseFactory('v8'),
   'category': CATEGORY_FYI,
   'auto_reboot' : False,
 }
 
 b_v8_linux_predictable = {
   'name': 'V8 Linux - predictable',
   'factory': m_annotator.BaseFactory('v8'),
   'category': CATEGORY_FYI + '|predictable',
   'auto_reboot' : False,
+  'mergeRequests': merge_requests_logarithmic,
 }
 
 b_v8_linux_interpreted_regexp = {
   'name': 'V8 Linux - interpreted regexp',
   'builddir': 'v8-linux-interpreted-regexp',
   'factory': m_annotator.BaseFactory('v8'),
   'category': CATEGORY_FYI,
   'auto_reboot' : False,
 }
 
@@ skipping 453 matching lines @@
 # too low. Must keep at least a few days worth of builds.
 c['buildHorizon'] = 1000
 c['logHorizon'] = 500
 # Must be at least 2x the number of slaves.
 c['eventHorizon'] = 200
 
 ####### PROJECT IDENTITY
 
 c['projectName'] = ActiveMaster.project_name
 c['projectURL'] = config.Master.project_url