Revert "[SYCL][L0] Re-enable round-robin submissions to multiple compute engines" (#6510)

This reverts commit 24e0b82.

Author: smaslov-intel

sycl/doc/EnvironmentVariables.md

@@ -155,7 +155,7 @@ variables in production code.</span>
 | `SYCL_PI_LEVEL_ZERO_COPY_BATCH_SIZE` | Integer | Sets a preferred number of copy commands to batch into a command list before executing the command list. A value of 0 causes the batch size to be adjusted dynamically. A value greater than 0 specifies fixed size batching, with the batch size set to the specified value. The default is 0. |
 | `SYCL_PI_LEVEL_ZERO_FILTER_EVENT_WAIT_LIST` | Integer | When set to 0, disables filtering of signaled events from wait lists when using the Level Zero backend. The default is 1. |
 | `SYCL_PI_LEVEL_ZERO_USE_COPY_ENGINE` | Any(\*) | This environment variable enables users to control use of copy engines for copy operations. If the value is an integer, it will allow the use of copy engines, if available in the device, in Level Zero plugin to transfer SYCL buffer or image data between the host and/or device(s) and to fill SYCL buffer or image data in device or shared memory. The value of this environment variable can also be a pair of the form "lower_index:upper_index" where the indices point to copy engines in a list of all available copy engines. The default is 1. |
-| `SYCL_PI_LEVEL_ZERO_USE_COMPUTE_ENGINE` | Integer | It can be set to an integer (>=0) in which case all compute commands will be submitted to the command-queue with the given index in the compute command group. If it is instead set to a negative value then all available compute engines may be used. The default value is "-1" |
+| `SYCL_PI_LEVEL_ZERO_USE_COMPUTE_ENGINE` | Integer | It can be set to an integer (>=0) in which case all compute commands will be submitted to the command-queue with the given index in the compute command group. If it is instead set to a negative value then all available compute engines may be used. The default value is "0" |
 | `SYCL_PI_LEVEL_ZERO_USE_COPY_ENGINE_FOR_D2D_COPY` (experimental) | Integer | Allows the use of copy engine, if available in the device, in Level Zero plugin for device to device copy operations. The default is 0. This option is experimental and will be removed once heuristics are added to make a decision about use of copy engine for device to device copy operations. |
 | `SYCL_PI_LEVEL_ZERO_DEVICE_SCOPE_EVENTS` | Any(\*) | Enable support of device-scope events whose state is not visible to the host. If enabled mode is SYCL_PI_LEVEL_ZERO_DEVICE_SCOPE_EVENTS=1 the Level Zero plugin would create all events having device-scope only and create proxy host-visible events for them when their status is needed (wait/query) on the host. If enabled mode is SYCL_PI_LEVEL_ZERO_DEVICE_SCOPE_EVENTS=2 the Level Zero plugin would create all events having device-scope and add proxy host-visible event at the end of each command-list submission. The default is 2, meaning only the last event in a batch is host-visible. |
 | `SYCL_PI_LEVEL_ZERO_USE_IMMEDIATE_COMMANDLISTS` | Integer | When set to a positive value enables use of Level Zero immediate commandlists, which means there is no batching and all commands are immediately submitted for execution. Default is 0. Note: When immediate commandlist usage is enabled it is necessary to also set SYCL_PI_LEVEL_ZERO_DEVICE_SCOPE_EVENTS to either 0 or 1.  |

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -393,14 +393,14 @@ class ReturnHelper {
 // with the given index in the compute command group. If it is instead set
 // to negative then all available compute engines may be used.
 //
-// The default value is "-1".
+// The default value is "0".
 //
 static const std::pair<int, int> getRangeOfAllowedComputeEngines = [] {
   const char *EnvVar = std::getenv("SYCL_PI_LEVEL_ZERO_USE_COMPUTE_ENGINE");
-  // If the environment variable is not set, all available compute engines
-  // can be used.
+  // If the environment variable is not set only use "0" CCS for now.
+  // TODO: allow all CCSs when HW support is complete.
   if (!EnvVar)
-    return std::pair<int, int>(0, INT_MAX);
+    return std::pair<int, int>(0, 0);
 
   auto EnvVarValue = std::atoi(EnvVar);
   if (EnvVarValue >= 0) {