Remove pipeline stall timing (and avoid Explorer perf regressions)

megatron/schedules.py

@@ -362,11 +362,6 @@ def forward_backward_pipelining_without_interleaving(forward_step_func, data_ite
     num_microbatches_remaining = \
         num_microbatches - num_warmup_microbatches
 
-    # Measure pipeline stall only if there are enough microbatches
-    # to have every worker in a warmup and steady state phase.
-    measure_pipeline_stall = get_num_microbatches() >= \
-        mpu.get_pipeline_model_parallel_world_size()
-
     input_tensors = []
     output_tensors = []
     losses_reduced = []
@@ -376,22 +371,11 @@ def forward_backward_pipelining_without_interleaving(forward_step_func, data_ite
         input_tensor = p2p_communication.recv_forward(timers)
         output_tensor = forward_step(forward_step_func, data_iterator, model,
                                      input_tensor, losses_reduced)
-        # Barrier before first receive to measure forward stall.
-        if i == (num_warmup_microbatches - 1) and measure_pipeline_stall:
-            timers('forward-pipeline-stall').start()
-            torch.distributed.barrier(group=mpu.get_pipeline_model_parallel_group())
-            timers('forward-pipeline-stall').stop()
         p2p_communication.send_forward(output_tensor, timers)
 
         input_tensors.append(input_tensor)
         output_tensors.append(output_tensor)
 
-    # Barrier before first receive to measure forward stall.
-    if num_warmup_microbatches == 0 and measure_pipeline_stall:
-        timers('forward-pipeline-stall').start()
-        torch.distributed.barrier(group=mpu.get_pipeline_model_parallel_group())
-        timers('forward-pipeline-stall').stop()
-
     # Before running 1F1B, need to receive first forward tensor.
     # If all microbatches are run in warmup / cooldown phase, then no need to
     # receive this tensor here.

megatron/training.py

@@ -356,11 +356,6 @@ def train_step(forward_step_func, data_iterator,
                                           fp32_allreduce=args.fp32_allreduce)
         timers('backward-params-all-reduce').stop()
 
-    # Barrier to measure backward stall.
-    timers('backward-pipeline-stall').start()
-    torch.distributed.barrier(group=mpu.get_pipeline_model_parallel_group())
-    timers('backward-pipeline-stall').stop()
-
     # All-reduce word_embeddings' grad across first and last stages to ensure
     # that word_embeddings parameters stay in sync.
     # This should only run for models that support pipelined model parallelism
@@ -451,12 +446,10 @@ def training_log(loss_dict, total_loss_dict, learning_rate, iteration,
         if name in timers.timers:
             timers_to_log.append(name)
     add_to_logging('forward-compute')
-    add_to_logging('forward-pipeline-stall')
     add_to_logging('forward-recv')
     add_to_logging('forward-send')
     add_to_logging('forward-backward-send-forward-backward-recv')
     add_to_logging('backward-compute')
-    add_to_logging('backward-pipeline-stall')
     add_to_logging('backward-recv')
     add_to_logging('backward-send')
     add_to_logging('backward-send-forward-recv')