Update IPEX_LLM_PERFORMANCE_MODE with input length threshold (#11908)

* Update IPEX_LLM_PERFORMANCE_MODE with input length threshold

* Update based on comments. And and judgement for inputs_embeds

* Fix for benchmarking purposes

* Update based on comments

* Small fix

python/llm/src/ipex_llm/transformers/lookup.py

@@ -40,6 +40,9 @@
 original_generate = GenerationMixin.generate
 query_group_size = 16
 
+# may tune it with more tested data
+PERFORMANCE_MODE_LOOKUP_INPUT_THRESHOLD = 100
+
 
 @torch.no_grad()
 def generate(
@@ -57,7 +60,14 @@ def generate(
     lookahead = kwargs.pop("lookahead", None)
     perf_mode = os.environ.get("IPEX_LLM_PERFORMANCE_MODE", None)
     if perf_mode == "1" and lookahead is None:
-        lookahead = 2  # default to 2 now
+        if inputs is not None:
+            if inputs.shape[1] >= PERFORMANCE_MODE_LOOKUP_INPUT_THRESHOLD:
+                lookahead = 2  # default to 2 now
+        else:
+            inputs_embeds = kwargs.get("inputs_embeds", None)
+            if inputs_embeds is not None:
+                if inputs_embeds.shape[1] >= PERFORMANCE_MODE_LOOKUP_INPUT_THRESHOLD:
+                    lookahead = 2  # default to 2 now
     if lookahead:
         from ipex_llm.transformers.convert import get_enable_ipex
         _enable_ipex = get_enable_ipex()