Factoring out device affinity generation to be used in swarming

telemetry/telemetry/util/bot_utils.py

Index: telemetry/telemetry/util/bot_utils.py
diff --git a/telemetry/telemetry/util/bot_utils.py b/telemetry/telemetry/util/bot_utils.py
new file mode 100644
index 0000000000000000000000000000000000000000..70955f5d3a4ab2e443df261d0c0c7d5ef9a2f7d2
--- /dev/null
+++ b/telemetry/telemetry/util/bot_utils.py
@@ -0,0 +1,27 @@
+# Copyright 2013 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.
+
+"""
+Utility functions used to generate info used by the bots.
+
+TODO(eyaich): Remove once we no longer generate the list of benchmarks to
+run on the perf waterfall in telemetry.
+"""
+
+import hashlib
+
+def GetDeviceAffinity(num_shards, base_name):
+  # Based on the current timings, we shift the result of the hash function to
+  # achieve better load balancing. Those shift values are to be revised when
+  # necessary. The shift value is calculated such that the total cycle time
+  # is minimized.
+  hash_shift = {
+    2 : 47,  # for old desktop configurations with 2 slaves
+    5 : 56,  # for new desktop configurations with 5 slaves
+    21 : 43  # for Android 3 slaves 7 devices configurations
+  }
+  shift = hash_shift.get(num_shards, 0)
+  base_name_hash = hashlib.sha1(base_name).hexdigest()
+  device_affinity = (int(base_name_hash, 16) >> shift) % num_shards
+  return device_affinity