[Docs] Add more details to profiling docs

docs/references/benchmark_and_profiling.md

@@ -15,8 +15,46 @@
   python3 -m sglang.bench_serving --backend sglang --num-prompt 10
   ```
 
+## Profile with PyTorch Profiler
+Pytorch Profiler is a convenient basic tool to inspect kernel execution time, call stack, and kernel overlap and occupancy.
+- To profile a server
+```bash
+# set trace path
+export SGLANG_TORCH_PROFILER_DIR=/root/sglang/profile_log
+
+# start server
+python -m sglang.launch_server --model-path meta-llama/Llama-3.1-8B-Instruct
+
+# send profiling request from client
+python -m sglang.bench_serving --backend sglang --model-path meta-llama/Llama-3.1-8B-Instruct --num-prompts 10 --sharegpt-output-len 100 --profile
+```
+Please make sure that the `SGLANG_TORCH_PROFILER_DIR` should be set at both server and client side, otherwise the trace file cannot be generated correctly . A secure way will be setting `SGLANG_TORCH_PROFILER_DIR` in the `.*rc` file of shell (e.g. `~/.bashrc` for bash shells).
+
+- To profile offline
+```bash
+export SGLANG_TORCH_PROFILER_DIR=/root/sglang/profile_log
+python -m sglang.bench_offline_throughput --model-path meta-llama/Llama-3.1-8B-Instruct --dataset-name random --num-prompts 10 --profile --mem-frac=0.8
+```
+
+- View Traces
+
+Trace files can be loaded and visualized from:
+1. https://ui.perfetto.dev/ (any browser)
+2. chrome://tracing (Chrome browser only)
+
+If browser cannot open trace file due to its large size,
+client can generate a small trace file (<100MB) by controlling number of prompts and lengths of prompt outputs.
+For example, when profiling a server,
+```bash
+python -m sglang.bench_serving --backend sglang --model-path meta-llama/Llama-3.1-8B-Instruct --num-prompts 2 --sharegpt-output-len 100 --profile
+```
+sets the number of prompts to 2 with `--num-prompts` argument and limits the length of output sequences to 100 with `--sharegpt-output-len` argument, which can generate a small trace file for browser to open smoothly.
+
 ## Profile with Nsight
-0. Prerequisite
+Nsight systems is an advanced tool that exposes more profiling details, such as register and shared memory usage, annotated code regions and low-level CUDA APIs and events.
+
+0. Prerequisite: install using apt, or run inside a [NVIDIA Docker container](https://catalog.ngc.nvidia.com/orgs/nvidia/containers/pytorch/tags) or [SGLang Docker container](https://github.com/sgl-project/sglang/tree/main/docker).
+
 ```bash
 # install nsys
 # https://docs.nvidia.com/nsight-systems/InstallationGuide/index.html
@@ -41,54 +79,21 @@ nsys profile --trace-fork-before-exec=true --cuda-graph-trace=node -o sglang.out
 python3 -m sglang.bench_serving --backend sglang --num-prompts 1000 --dataset-name random --random-input 1024 --random-output 512
 ```
 
-3. Use NVTX, e.g.
+3. Use NVTX to annotate code regions, e.g. to see their execution time.
 
 ```bash
 # install nvtx
 pip install nvtx
-
+```
+``` python
 # code snippets
 import nvtx
 with nvtx.annotate("description", color="color"):
     # some critical code
 ```
 
 ## Other tips
-
 1. You can benchmark a model using dummy weights by only providing the config.json file. This allows for quick testing of model variants without training. To do so, add `--load-format dummy` to the above commands and then you only need a correct `config.json` under the checkpoint folder.
 2. You can benchmark a model with modified configs (e.g., less layers) by using `--json-model-override-args`. For example, you can benchmark a model with only 2 layers and 2 kv heads using `python -m sglang.bench_one_batch --model-path meta-llama/Meta-Llama-3.1-8B-Instruct --batch 32 --input-len 256 --output-len 32 --load-format dummy --json-model-override-args '{"num_hidden_layers": 1, "num_key_value_heads": 1}'`
-
-
-## Profile with PyTorch Profiler
-- To profile a server
-```bash
-# set trace path
-export SGLANG_TORCH_PROFILER_DIR=/root/sglang/profile_log
-
-# start server
-python -m sglang.launch_server --model-path meta-llama/Llama-3.1-8B-Instruct
-
-# send profiling request from client
-python -m sglang.bench_serving --backend sglang --model-path meta-llama/Llama-3.1-8B-Instruct --num-prompts 10 --sharegpt-output-len 100 --profile
-```
-Please make sure that the `SGLANG_TORCH_PROFILER_DIR` should be set at both server and client side, otherwise the trace file cannot be generated correctly . A secure way will be setting `SGLANG_TORCH_PROFILER_DIR` in the `.*rc` file of shell (e.g. `~/.bashrc` for bash shells).
-
-- To profile offline
-```bash
-export SGLANG_TORCH_PROFILER_DIR=/root/sglang/profile_log
-python -m sglang.bench_offline_throughput --model-path meta-llama/Llama-3.1-8B-Instruct --dataset-name random --num-prompts 10 --profile --mem-frac=0.8
-```
-
-- View Traces
-
-Trace files can be loaded and visualized from:
-1. https://ui.perfetto.dev/ (any browser)
-2. chrome://tracing (Chrome browser only)
-
-If browser cannot open trace file due to its large size,
-client can generate a small trace file (<100MB) by controlling number of prompts and lengths of prompt outputs.
-For example, when profiling a server,
-```bash
-python -m sglang.bench_serving --backend sglang --model-path meta-llama/Llama-3.1-8B-Instruct --num-prompts 2 --sharegpt-output-len 100 --profile
-```
-sets the number of prompts to 2 with `--num-prompts` argument and limits the length of output sequences to 100 with `--sharegpt-output-len` argument, which can generate a small trace file for browser to open smoothly.
+3. You can use `--python-backtrace=cuda` to see python call stack for all CUDA kernels, as in PyTorch Profiler. (Caveat: this can cause inaccurately long kernel runtimes for CUDA event based timing)
+4. For more args please see https://docs.nvidia.com/nsight-systems/UserGuide/index.html