bugfix: only check backend when mode == Collecive (#36758)

* bugfix: only check backend when mode == Collecive * fix bug

Author: 2742195759

python/paddle/distributed/fleet/launch.py

@@ -334,7 +334,20 @@ def launch_ps(args, distribute_mode):
  return
 
 
+def infer_backend(args):
+ if args.backend != "auto": return
+ if fluid.core.is_compiled_with_cuda():
+ args.backend = 'nccl'
+ elif fluid.core.is_compiled_with_npu():
+ args.backend = 'unknown'
+ elif fluid.core.is_compiled_with_xpu():
+ args.backend = 'bkcl'
+ else:
+ args.backend = 'gloo'
+
+
 def which_distributed_mode(args):
+ infer_backend(args) # modify the args.backend
  if args.run_mode is not None:
  assert args.run_mode in ["collective", "ps", "ps-heter"]
 
@@ -368,12 +381,9 @@ def which_distributed_mode(args):
 
  if fluid.core.is_compiled_with_cuda():
  accelerators = fluid.core.get_cuda_device_count()
- args.backend = 'nccl'
  elif fluid.core.is_compiled_with_npu():
- args.backend = 'unknown'
  accelerators = fluid.core.get_npu_device_count()
  elif fluid.core.is_compiled_with_xpu():
- args.backend = 'bkcl'
  accelerators = fluid.core.get_xpu_device_count()
  else:
  accelerators = 0
@@ -400,7 +410,6 @@ def which_distributed_mode(args):
 But found args.servers not empty, default use ps mode")
  return DistributeMode.PS
  else:
- args.backend = "gloo"
  return DistributeMode.COLLECTIVE
  else:
  logger.warning(
@@ -583,20 +592,21 @@ def launch():
  _print_arguments(args)
 
  if args.backend == 'auto':
- distribute_mode = which_distributed_mode(args)
- assert args.backend in [
- 'gloo', 'nccl', 'bkcl', 'unknown'
- ] # which_distributed_mode must modify args.backend
+ distribute_mode = which_distributed_mode(
+ args) # which_distributed_mode must modify args.backend
  else:
  assert args.run_mode == 'collective' or args.run_mode == None, "When backend is not 'auto', run mode must be collective"
  check_backend(args.backend)
  distribute_mode = DistributeMode.COLLECTIVE
 
- block_windows_and_macos(
- args.backend) # raise error when using gloo on windows or macos
+ assert args.backend in ['gloo', 'nccl', 'bkcl', 'unknown']
+
  if args.backend == 'gloo':
  logger.warning("launch start with CPUONLY mode")
 
+ block_windows_and_macos(
+ args.backend) # raise error when using gloo on windows or macos
+
  if enable_elastic(args, distribute_mode):
  launch_elastic(args, distribute_mode)
  return