feat: improve temperature logic in chat (#1749)

This PR adds support for `do_sample` to chat to enable greedy sampling

---------
Co-authored-by: Nicolas Patry <patry.nicolas@protonmail.com>

router/src/server.rs

@@ -1000,6 +1000,7 @@ async fn chat_completions(
         tools,
         tool_choice,
         tool_prompt,
+        temperature,
         ..
     } = req;
 
@@ -1008,6 +1009,11 @@ async fn chat_completions(
     let logprobs = logprobs.unwrap_or(false);
     let tool_prompt = tool_prompt.unwrap_or_default();
     let stop = stop.unwrap_or_default();
+    // enable greedy only when temperature is 0
+    let (do_sample, temperature) = match temperature {
+        Some(temperature) if temperature == 0.0 => (false, None),
+        other => (true, other),
+    };
 
     // extract tool grammar if present
     let tool_grammar = match ToolGrammar::apply(tools, tool_choice) {
@@ -1054,13 +1060,13 @@ async fn chat_completions(
         inputs: inputs.to_string(),
         parameters: GenerateParameters {
             best_of: None,
-            temperature: req.temperature,
+            temperature,
             repetition_penalty,
             frequency_penalty: req.frequency_penalty,
             top_k: None,
             top_p: req.top_p,
             typical_p: None,
-            do_sample: true,
+            do_sample,
             max_new_tokens,
             return_full_text: None,
             stop,

server/text_generation_server/utils/tokens.py

@@ -273,7 +273,7 @@ class HeterogeneousNextTokenChooser:
             else None
         )
 
-        if any([x != 1.0 for x in temperature]):
+        if any(x != 1.0 for x in temperature):
             do_sample = [
                 sample or x != 1.0 for x, sample in zip(temperature, do_sample)
             ]
@@ -281,15 +281,15 @@ class HeterogeneousNextTokenChooser:
                 HeterogeneousTemperatureLogitsWarper(temperature, dtype, device)
             )
 
-        if any([x != 0 for x in top_k]):
+        if any(x != 0 for x in top_k):
             do_sample = [sample or x != 0 for x, sample in zip(top_k, do_sample)]
             warpers.append(HeterogeneousTopKLogitsWarper(top_k, device))
 
-        if any([x < 1.0 for x in top_p]):
+        if any(x < 1.0 for x in top_p):
             do_sample = [sample or x < 1.0 for x, sample in zip(top_p, do_sample)]
             warpers.append(HeterogeneousTopPLogitsWarper(top_p, dtype, device))
 
-        if any([x < 1.0 for x in typical_p]):
+        if any(x < 1.0 for x in typical_p):
             do_sample = [sample or x < 1.0 for x, sample in zip(typical_p, do_sample)]
             warpers.append(HeterogeneousTypicalLogitsWarper(typical_p, dtype, device))