[L0] zeDeviceCanAccessPeer call optimization

The more cards used, zeDeviceCanAccessPeer time costing is becoming
more and more expensive. Improved by caching p2p devices status thus
reducing the number of zeDeviceCanAccessPeer calling times.

Signed-off-by: Winston Zhang <[email protected]>

Author: winstonzhang-intel

source/adapters/level_zero/context.hpp

@@ -100,6 +100,9 @@ struct ur_context_handle_t_ : _ur_object {
                                          l0_command_list_cache_info>>>
       ZeCopyCommandListCache;
 
+  std::unordered_map<ur_device_handle_t, std::list<ur_device_handle_t>>
+      P2PDeviceCache;
+
   // Store USM pool for USM shared and device allocations. There is 1 memory
   // pool per each pair of (context, device) per each memory type.
   std::unordered_map<ze_device_handle_t, umf::pool_unique_handle_t>

source/adapters/level_zero/usm.cpp

@@ -153,15 +153,26 @@ static ur_result_t USMAllocationMakeResident(
   } else {
     Devices.push_back(Device);
     if (ForceResidency == USMAllocationForceResidencyType::P2PDevices) {
-      ze_bool_t P2P;
-      for (const auto &D : Context->Devices) {
-        if (D == Device)
-          continue;
-        // TODO: Cache P2P devices for a context
-        ZE2UR_CALL(zeDeviceCanAccessPeer,
-                   (D->ZeDevice, Device->ZeDevice, &P2P));
-        if (P2P)
-          Devices.push_back(D);
+      // Check if the P2P devices are already cached
+      auto it = Context->P2PDeviceCache.find(Device);
+      if (it != Context->P2PDeviceCache.end()) {
+        // Use cached P2P devices
+        Devices.insert(Devices.end(), it->second.begin(), it->second.end());
+      } else {
+        // Query for P2P devices and update the cache
+        std::list<ur_device_handle_t> P2PDevices;
+        ze_bool_t P2P;
+        for (const auto &D : Context->Devices) {
+          if (D == Device)
+            continue;
+          ZE2UR_CALL(zeDeviceCanAccessPeer,
+                     (D->ZeDevice, Device->ZeDevice, &P2P));
+          if (P2P)
+            P2PDevices.push_back(D);
+        }
+        // Update the cache
+        Context->P2PDeviceCache[Device] = P2PDevices;
+        Devices.insert(Devices.end(), P2PDevices.begin(), P2PDevices.end());
       }
     }
   }