Add env var to enable / disable the immediate append path

Author: Fabio Mestre

source/adapters/level_zero/command_buffer.cpp

@@ -35,6 +35,39 @@ bool checkImmediateAppendSupport(ur_context_handle_t Context,
       Context->getPlatform()->isDriverVersionNewerOrSimilar(1, 3,
                                                             MinDriverVersion);
 
+  // If this environment variable is:
+  //   - Set to 1: the immediate append path will always be enabled as long the
+  //   pre-requisites are met.
+  //   - Set to 0: the immediate append path will always be disabled.
+  //   - Not Defined: The default behaviour will be used which enables the
+  //   immediate append path only for some devices when the pre-requisites are
+  //   met.
+  const char *AppendEnvVarName = "UR_L0_CMD_BUFFER_USE_IMMEDIATE_APPEND_PATH";
+  const char *UrRet = std::getenv(AppendEnvVarName);
+
+  if (UrRet) {
+    const bool EnableAppendPath = std::atoi(UrRet) == 1;
+
+    if (EnableAppendPath && !Device->ImmCommandListUsed) {
+      logger::error("{} is set but immediate command-lists are currently "
+                    "disabled. Immediate command-lists are "
+                    "required to use the immediate append path.",
+                    AppendEnvVarName);
+      std::abort();
+    }
+    if (EnableAppendPath && !DriverSupportsImmediateAppend) {
+      logger::error("{} is set but "
+                    "the current driver does not support the "
+                    "zeCommandListImmediateAppendCommandListsExp entrypoint. A "
+                    "driver version of at least {} is required to use the "
+                    "immediate append path.",
+                    AppendEnvVarName, MinDriverVersion);
+      std::abort();
+    }
+
+    return EnableAppendPath;
+  }
+
   return Device->isPVC() && Device->ImmCommandListUsed &&
          DriverSupportsImmediateAppend;
 }
@@ -1670,7 +1703,7 @@ ur_result_t validateCommandDesc(
   logger::debug("Mutable features supported by device {}", SupportedFeatures);
 
   // Kernel handle updates are not yet supported.
-  if (CommandDesc->hNewKernel != Command->Kernel) {
+  if (CommandDesc->hNewKernel && CommandDesc->hNewKernel != Command->Kernel) {
     return UR_RESULT_ERROR_UNSUPPORTED_FEATURE;
   }
 
@@ -1959,11 +1992,7 @@ ur_result_t updateKernelCommand(
  */
 ur_result_t
 waitForOngoingExecution(ur_exp_command_buffer_handle_t CommandBuffer) {
-
-  bool UsingImmediateAppendPath = checkImmediateAppendSupport(
-      CommandBuffer->Context, CommandBuffer->Device);
-
-  if (UsingImmediateAppendPath) {
+  if (CommandBuffer->UseImmediateAppendPath) {
     if (ur_event_handle_t &CurrentSubmissionEvent =
             CommandBuffer->CurrentSubmissionEvent) {
       ZE2UR_CALL(zeEventHostSynchronize,