!10812 bugfix: ps cache data process performance decay

From: @zyli2020
Reviewed-by: @cristoval,@limingqi107
Signed-off-by: @cristoval

mindspore/parallel/_ps_context.py

@@ -14,6 +14,7 @@
 # ============================================================================
 """Context for parameter server training mode"""
 
+import os
 from mindspore._c_expression import PSContext
 
 _ps_context = None
@@ -134,4 +135,10 @@ def _clone_hash_table(dest_param_name, src_param_name):
     ps_context().clone_hash_table(dest_param_name, src_param_name)
 
 def _set_cache_enable(cache_enable):
+    # Environment variables are used to specify a maximum number of OpenBLAS threads:
+    # In ubuntu(GPU) environment, numpy will use too many threads for computing,
+    if cache_enable:
+        os.environ['OPENBLAS_NUM_THREADS'] = '2'
+        os.environ['GOTO_NUM_THREADS'] = '2'
+        os.environ['OMP_NUM_THREADS'] = '2'
     ps_context().set_cache_enable(cache_enable)