From 5ad237b63051264853efcbd1a4830034ed7e10f9 Mon Sep 17 00:00:00 2001
From: Kaipeng Deng <dengkaipeng@baidu.com>
Date: Fri, 28 Jun 2019 20:22:11 +0800
Subject: [PATCH] not enable sync bn in single device (#2607)

---
 tools/train.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/train.py b/tools/train.py
index 242846986..037decdcc 100644
--- a/tools/train.py
+++ b/tools/train.py
@@ -126,7 +126,8 @@ def main():
     build_strategy.memory_optimize = False
     build_strategy.enable_inplace = True
     sync_bn = getattr(model.backbone, 'norm_type', None) == 'sync_bn'
-    build_strategy.sync_batch_norm = sync_bn
+    # only enable sync_bn in multi-devices
+    build_strategy.sync_batch_norm = sync_bn and devices_num > 1
     train_compile_program = fluid.compiler.CompiledProgram(
         train_prog).with_data_parallel(
             loss_name=loss.name, build_strategy=build_strategy)
-- 
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