Add Elasticity Support via NIXL Integration

NIXL_README.md

@@ -0,0 +1,100 @@
+# DeepEP with NIXL - Build and Setup Guide
+
+## Overview
+
+This guide covers building and running DeepEP with NIXL integration, which enables **elastic scaling capabilities** for dynamic addition and removal of processes (ranks) during runtime.
+
+### Build Dependencies
+
+Follow the build instructions in the [NIXL repository](https://github.com/ai-dynamo/nixl) to install:
+- **NIXL** (NVIDIA Inference Xfer Library)
+- **UCX** (Unified Communication X)
+- **ETCD** and ETCD C++ client library
+- **DOCA** (with GPUNetIO)
+
+## Building DeepEP with NIXL
+
+### Step 1: Configure Environment Variables
+
+Edit `scripts/set_env.sh` to match your installation paths and source the environment:
+```bash
+source scripts/set_env.sh
+```
+
+### Step 2: Build DeepEP with NIXL
+
+Edit the paths in `scripts/build.sh` to match your installation paths and build DeepEP using the provided build script:
+
+```bash
+./scripts/build.sh
+```
+
+**Build output**:
+- Compiled library: `build/lib.linux-x86_64-3.10/deep_ep_cpp.cpython-310-x86_64-linux-gnu.so`
+
+## Running Elastic Tests
+
+### Adjust UCX Network Devices
+
+Edit `tests/elastic/elastic.py` / `tests/test_internode.py` to adjust the UCX network devices to match your system:
+```python
+pxb_nics = ["mlx5_0", "mlx5_3", "mlx5_4", "mlx5_5", "mlx5_6", "mlx5_9", "mlx5_10", "mlx5_11"]
+tcp_nics = ',ibp154s0,ibp192s0,ibp206s0,ibp220s0,ibp94s0'
+os.environ['UCX_NET_DEVICES'] = f'cuda{local_rank}-{pxb_nics[local_rank]}:1' + tcp_nics
+```
+
+**Note**: This is a workaround to force UCX to chose correct network devices on some systems.
+
+### Start ETCD Server
+
+If not already running:
+```bash
+# Local test (single node)
+etcd --listen-client-urls http://127.0.0.1:2379 --advertise-client-urls http://127.0.0.1:2379
+
+# Multi-node setup (on master node)
+etcd --listen-client-urls http://0.0.0.0:2379 --advertise-client-urls http://<MASTER_IP>:2379
+```
+
+### Set Runtime Environment
+
+```bash
+export UCX_LOG_LEVEL=error
+export LD_PRELOAD=$DOCA_HOME/lib/x86_64-linux-gnu/libdoca_common.so:$DOCA_HOME/lib/x86_64-linux-gnu/libdoca_gpunetio.so:$DOCA_HOME/lib/x86_64-linux-gnu/libdoca_verbs.so
+export LD_LIBRARY_PATH=$UCX_HOME/lib:$LD_LIBRARY_PATH
+```
+
+### Run Elastic Scaling Test
+
+#### Single Node (8 ranks, 4→8 expansion):
+```bash
+python3 tests/elastic/elastic.py \
+    --plan tests/elastic/single_expansion.json \
+    --num-processes 8 \
+    --etcd-server http://127.0.0.1:2379
+```
+
+#### Multi-Node Setup:
+
+**Node 1** (will launch the first phase with 4 ranks):
+```bash
+python3 tests/elastic/elastic.py \
+    --plan tests/elastic/single_expansion.json \
+    --num-processes 4 \
+```
+
+**Node 2** (will join the second phase with additional 4 ranks):
+```bash
+python3 tests/elastic/elastic.py \
+    --plan tests/elastic/single_expansion.json \
+    --num-processes 4 \
+    --rank-server $MASTER_IP \
+    --etcd-server http://$MASTER_IP:2379
+```
+
+### Available Test Plans
+
+- `no_expansion.json`: Static 4 ranks (baseline)
+- `single_expansion.json`: 4 → 8 ranks (single expansion)
+- `double_expansion.json`: 4 → 6 → 8 ranks (two expansions)
+- `expansion_contraction.json`: 4 → 8 → 6 ranks (scale up then down)

csrc/config.hpp

@@ -56,9 +56,7 @@ struct Config {
         size_t num_bytes = 0;
         num_bytes += num_channels * num_nvl_ranks * (2 * num_rdma_ranks + 3) * sizeof(int);
         num_bytes += num_channels * num_nvl_ranks * num_max_nvl_chunked_recv_tokens * hidden_bytes;
-#ifndef DISABLE_NVSHMEM
         num_bytes += num_channels * num_nvl_ranks * num_max_nvl_chunked_recv_tokens * internode::get_source_meta_bytes();
-#endif
         num_bytes += num_channels * num_nvl_ranks * num_max_nvl_chunked_recv_tokens * kNumMaxTopK * sizeof(int64_t);
         num_bytes += num_channels * num_nvl_ranks * num_max_nvl_chunked_recv_tokens * kNumMaxTopK * sizeof(float);
         num_bytes += num_channels * num_nvl_ranks * num_max_nvl_chunked_recv_tokens * kNumMaxScales * sizeof(float);
@@ -67,7 +65,6 @@ struct Config {
     }
 
     size_t get_rdma_buffer_size_hint(int64_t hidden_bytes, int num_ranks) const {
-#ifndef DISABLE_NVSHMEM
         // Legacy mode
         if (num_ranks <= NUM_MAX_NVL_PEERS)
             return 0;
@@ -91,9 +88,6 @@ struct Config {
         num_bytes += num_channels * num_rdma_ranks * num_max_rdma_chunked_recv_tokens * sizeof(int4) * 2;
         num_bytes = ((num_bytes + 127) / 128) * 128;
         return num_bytes;
-#else
-        EP_HOST_ASSERT(false and "NVSHMEM is disable during compilation");
-#endif
     }
 };