[Platform] Fix CPU binding logic (#6889)

### What this PR does / why we need it?

- Rework CpuAlloc.handle_no_affinity() to build available NUMA nodes
after allowed_cpus filtering, assign NPUs to NUMA nodes via round‑robin,
and split CPUs per NPU with disjoint slices for better balance.
- Improve bind_memory() robustness by deriving the target NUMA from each
NPU’s CPU pool, validating NUMA existence, and skipping binding when
data is missing.
- bind_memory() now only bind the single NUMA node that corresponds to
NPU id, instead of 2 NUMA nodes.
- Fix the issue that all NPUs bind to 0th NUMA node when DP16 due to
global NPU id is not visible across DP domain.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Added/updated unit tests:

test_cpu_binding.py
1.   test_binding_mode_table covers A2 vs A3 binding mode mapping.
2. test_build_cpu_pools_fallback_to_numa_balanced covers fallback when
affinity info is missing.
3. TestBindingSwitch.test_is_arm_cpu covers ARM/x86/unknown arch
detection.
4.   test_bind_cpus_skip_non_arm covers non‑ARM skip path in bind_cpus.

test_worker_v1.py
1. Updated mocks for enable_cpu_binding default True to align with new
config default.

- vLLM version: v0.16.0
- vLLM main:
15d76f74e2

Signed-off-by: chenchuw886 <chenchuw@huawei.com>
Co-authored-by: chenchuw886 <chenchuw@huawei.com>

vllm_ascend/cpu_binding.py

@@ -209,38 +209,75 @@ class CpuAlloc:
             raise RuntimeError("lscpu command output error, no NUMA node available. Please check!")
 
     def handle_no_affinity(self) -> None:
-        num_running_npu = len(self.device_info.running_npu_list)
-        num_numa_node = len(self.numa_to_cpu_map)
-        if num_numa_node == 0 or num_running_npu == 0:
+        """
+        1) Build available NUMA nodes after allowed_cpus filtering
+        2) Assign NPUs to NUMA nodes by round-robin (npu_id % num_nodes)
+        3) Within each NUMA node, split its CPU list into per-NPU disjoint slices
+        """
+        running = list(self.device_info.running_npu_list)
+        if not running or not self.numa_to_cpu_map:
             return
-        if num_running_npu % num_numa_node != 0:
-            npu_num_per_node = num_running_npu // num_numa_node + 1
-        else:
-            npu_num_per_node = num_running_npu // num_numa_node
-        index = 0
+
+        # 1) Only keep NUMA nodes that still have CPUs after allowed_cpus filtering.
+        available_nodes: list[tuple[int, list[int]]] = []
         for node in sorted(self.numa_to_cpu_map):
-            # Available CPUs on this NUMA (constrained by allowed_cpus)
             cpus = [c for c in self.numa_to_cpu_map[node] if c in self.device_info.allowed_cpus]
-            if not cpus:
+            if cpus:
+                available_nodes.append((node, cpus))
+        if not available_nodes:
+            return
+
+        num_nodes = len(available_nodes)
+
+        # Infer "my_npu" from local rank + visible running_npu_list, assuming local rank is index into running_npu_list.
+        if 0 <= self.rank_id < len(running):
+            my_npu = running[self.rank_id]
+        else:
+            # Fallback: modulo in case rank range is larger than visible list length.
+            my_npu = running[self.rank_id % len(running)]
+
+        print(
+            f"[no_affinity_fine] rank:{self.rank_id} -> my_npu:{my_npu}; "
+            f"running_npu_list:{running}; num_available_nodes:{num_nodes}"
+        )
+
+        # 2) Round-robin assign NPUs to nodes based on NPU id (same as new logic).
+        # Build: node_index -> list[npu]
+        node_to_npus: dict[int, list[int]] = {i: [] for i in range(num_nodes)}
+        for npu in running:
+            node_index = npu % num_nodes
+            node_to_npus[node_index].append(npu)
+
+        # 3) Within each node, split cpus among the NPUs assigned to this node.
+        for node_index, npus in node_to_npus.items():
+            if not npus:
                 continue
-            # The actual number of NPUs to be allocated on this NUMA.
-            npu_num_this_node = min(npu_num_per_node, num_running_npu - index)
-            if npu_num_this_node <= 0:
-                break
-            # NUMA-balanced distribute the CPUs of this NUMA node among npu_num_this_node NPUs.
+
+            node_id, cpus = available_nodes[node_index]
             total_cpu_num = len(cpus)
-            base_cpu_num = total_cpu_num // npu_num_this_node
-            extra_cpu_num = total_cpu_num % npu_num_this_node
-            start_index = 0
-            for i in range(npu_num_this_node):
-                take_cpu_num = base_cpu_num + (1 if i < extra_cpu_num else 0)
-                end_index = start_index + take_cpu_num
-                select_cpus_list = cpus[start_index:end_index]
-                if index < num_running_npu:
-                    npu = self.device_info.running_npu_list[index]
-                    self.npu_cpu_pool[npu] = select_cpus_list
-                    index += 1
-                start_index = end_index
+            n = len(npus)
+
+            # Edge case: should not happen because we filtered cpus, but keep safe.
+            if total_cpu_num == 0:
+                continue
+
+            # If CPUs are fewer than NPUs, we can only guarantee small (possibly duplicated) slices.
+            if total_cpu_num < n:
+                for i, npu in enumerate(npus):
+                    cpu = cpus[i % total_cpu_num]
+                    self.npu_cpu_pool[npu] = [cpu]
+                continue
+
+            # Even split (disjoint slices), first 'extra' NPUs take 1 more CPU.
+            base = total_cpu_num // n
+            extra = total_cpu_num % n
+
+            start = 0
+            for i, npu in enumerate(npus):
+                take = base + (1 if i < extra else 0)
+                end = start + take
+                self.npu_cpu_pool[npu] = cpus[start:end]
+                start = end
 
     DEVICE_BINDING_MODE = {
         AscendDeviceType.A3: "numa_balanced",
@@ -302,15 +339,34 @@ class CpuAlloc:
         logger.info(f"NPU{current_npu}: main=[{main}]  acl=[{acl}]  release=[{rel}]")
 
     def bind_memory(self, pid: str, npu: int) -> None:
+        def _get_npu_numa_node(npu_id: int) -> int | None:
+            cpu_pool = self.npu_cpu_pool.get(npu_id, [])
+            if not cpu_pool:
+                return None
+            anchor_cpu = cpu_pool[0]
+            return self.cpu_node.get(anchor_cpu)
+
         if not shutil.which("migratepages"):
             logger.info("The 'migratepages' command is not available, skipping memory binding.")
             return
+        target_numa = _get_npu_numa_node(npu)
+        if target_numa is None:
+            logger.warning(f"[migrate] rank:{self.rank_id} -> NPU{npu} has no CPU pool, skip memory binding.")
+            return
         all_numa_nodes = sorted(self.numa_to_cpu_map.keys())
-        target_cpu = self.assign_acl[npu][0]
-        target_numa = self.cpu_node[target_cpu]
-        bind_numa_list = [target_numa, target_numa + 1 if target_numa % 2 == 0 else target_numa - 1]
-        logger.info(f"[migrate] rank:{self.rank_id} -> NUMA {bind_numa_list}")
-        execute_command(["migratepages", pid, ",".join(map(str, all_numa_nodes)), ",".join(map(str, bind_numa_list))])
+        if target_numa not in all_numa_nodes:
+            logger.warning(f"[migrate] NPU:{npu} -> NUMA {target_numa} not found, skip memory binding.")
+            return
+        # Bind memory to the NPU's NUMA node only to minimize cross-NUMA traffic.
+        logger.info(f"[migrate] NPU:{npu} -> NUMA [{target_numa}]")
+        execute_command(
+            [
+                "migratepages",
+                pid,
+                ",".join(map(str, all_numa_nodes)),
+                str(target_numa),
+            ]
+        )
 
     def bind_threads(self) -> None:
         thread_message, _ = execute_command(["ps", "-Te"])