Enable merging buildbot builds dependent on queue length

masters/master.client.v8/master.cfg

Index: masters/master.client.v8/master.cfg
diff --git a/masters/master.client.v8/master.cfg b/masters/master.client.v8/master.cfg
index 16311011017ed67bc1e2a6dc8f1cabaee2b58a53..1444d0f7e4096eaecced0fa285fe54f7d3edf64e 100644
--- a/masters/master.client.v8/master.cfg
+++ b/masters/master.client.v8/master.cfg
@@ -5,6 +5,8 @@
 # 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
 
@@ -17,6 +19,7 @@ from master.factory import annotator_factory
 import config
 import master_site_config
 
+import math
 import os
 
 
@@ -28,6 +31,19 @@ MAIL_NOTIFIER = ActiveMaster.is_production_host
 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
 
@@ -225,6 +241,7 @@ b_v8_linux_predictable = {
   'factory': m_annotator.BaseFactory('v8'),
   'category': CATEGORY_FYI + '|predictable',
   'auto_reboot' : False,
+  'mergeRequests': merge_requests_logarithmic,
 }
 
 b_v8_linux_interpreted_regexp = {