[SYCL][PI][L0] Increase start batch size from 2 to 4. (#2814)

This change-set ups the dynamic batch size start from 2 to 4.
This change recovers a performance regression that was noted
when the value was set at 2.

Author: kbsmith-intel

sycl/plugins/level_zero/pi_level_zero.hpp

@@ -277,8 +277,8 @@ struct _pi_context : _pi_object {
   std::mutex NumEventsLiveInEventPoolMutex;
 };
 
-// If doing dynamic batching, start batch size at 2.
-const pi_uint32 DynamicBatchStartSize = 2;
+// If doing dynamic batching, start batch size at 4.
+const pi_uint32 DynamicBatchStartSize = 4;
 
 struct _pi_queue : _pi_object {
   _pi_queue(ze_command_queue_handle_t Queue, pi_context Context,

sycl/test/plugins/level_zero_dynamic_batch_test.cpp

@@ -17,8 +17,8 @@
 // it does that 5 times as well.  That should cause the batch size to
 // be lowered, just once to be less than 4.
 //
-// CKDYN: Raising QueueBatchSize to 3
-// CKDYN: Raising QueueBatchSize to 4
+// CKDYN: Raising QueueBatchSize to 5
+// CKDYN: Raising QueueBatchSize to 6
 // CKDYN-NOT: Raising QueueBatchSize
 // CKALL: Test Pass
 // CKALL: Test Pass