[FEATURE] Add Profile Trace Merger for Distributed Traces (#11413)

docs/developer_guide/benchmark_and_profiling.md

@@ -74,6 +74,47 @@ python3 -m sglang.test.send_one
 python3 -m sglang.profiler
 ```
 
+### Profiler Trace Merger for Distributed Traces
+
+SGLang now supports automatic merging of profiling traces from distributed setups with multiple parallelism types (TP, DP, PP, EP). This feature is particularly useful for analyzing performance across distributed runs.
+
+#### Multi-Node Profiling and Shared Storage Considerations
+
+Single-node profiler output merging is completely supported. When profiling in distributed environments spanning multiple nodes, shared storage (e.g., NFS, Lustre) should be accessible by all nodes for the output directory to enable merging of trace files.
+
+If there is no shared storage accessible across nodes, automatic merging of trace files during profiling is not supported directly as of now.
+
+#### HTTP API Usage
+
+```bash
+# Start profiling with automatic trace merging enabled
+curl -X POST <BASE_URL>/start_profile \
+  -H "Content-Type: application/json" \
+  -d '{
+    "output_dir": "/tmp/profiles", # where to store profile traces
+    "num_steps": 10,
+    "activities": ["CPU", "GPU"],
+    "merge_profiles": true # optional argument to merge profile traces (default=False)
+  }'
+```
+
+#### Command Line Usage
+
+```bash
+# Start profiling with merge enabled
+python -m sglang.profiler \
+  --num-steps 10 \
+  --activities CPU GPU \
+  --output-dir /tmp/profiles \
+  --merge-profiles # optional argument to merge profile traces (default=False)
+```
+
+#### Output Files
+
+The profile merger generates:
+- Individual rank trace files: `{profile_id}-TP-{tp}-DP-{dp}-PP-{pp}-EP-{ep}.trace.json.gz`
+- Merged trace file: `merged-{profile_id}.trace.json.gz`
+
 ### Possible PyTorch bugs
 If in any cases you encounter the following error (for example, using qwen 2.5 VL):
 ```bash