Pull request replay

cfregly/ai-performance-engineering #10

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ch4/distallreduce.py

Fix NCCL hang in distallreduce.py: assign correct GPU per rank

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code/ch04/dist_allreduce.py0/2 exact hunks

code/ch04/dist_allreduce.py

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@@ -42,7 +42,9 @@ def main():

weakfile overlap

         print(f"Failed to initialize process group: {e}", flush=True)
         print("Running single-process benchmark instead.", flush=True)
         # Single process benchmark
-        device = "cuda" if args.backend == "nccl" and torch.cuda.is_available() else "cpu"
+        device = f"cuda:{rank}" if args.backend == "nccl" else "cpu"
+        if args.backend == "nccl":

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Open code/ch04/dist_allreduce.py at line 42

@@ -59,7 +61,9 @@ def main():

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     world_size = dist.get_world_size()
     
     # Allocate a large tensor
-    device = "cuda" if args.backend == "nccl" else "cpu"
+    device = f"cuda:{rank}" if args.backend == "nccl" else "cpu"
+    if args.backend == "nccl":

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Open code/ch04/dist_allreduce.py at line 61

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