remove floats == 0 comparison (vllm-project#285)

vllm/model_executor/layers/sampler.py

@@ -11,6 +11,7 @@
 from vllm.sampling_params import SamplingParams
 from vllm.sequence import SequenceOutputs
 
+_SAMPLING_EPS = 1e-5
 
 class Sampler(nn.Module):
     """Samples the next tokens from the model's outputs.
@@ -74,7 +75,7 @@ def forward(
         # Apply top-p and top-k truncation.
         top_ps, top_ks = _get_top_p_top_k(input_metadata, self.vocab_size)
         assert len(top_ps) == len(top_ks) == probs.shape[0]
-        if any(p < 1.0 for p in top_ps) or any(k != self.vocab_size for k in top_ks):
+        if any(p < 1.0 - _SAMPLING_EPS for p in top_ps) or any(k != self.vocab_size for k in top_ks):
             probs = _apply_top_p_top_k(probs, top_ps, top_ks)
 
         # Sample the next tokens.
@@ -152,7 +153,7 @@ def _apply_penalties(
             continue
         p = presence_penalties[i]
         f = frequency_penalties[i]
-        if p == 0.0 and f == 0.0:
+        if p < _SAMPLING_EPS and f < _SAMPLING_EPS:
             continue
         indices.append(i)
 
@@ -190,7 +191,7 @@ def _get_temperatures(
     for i, seq_group in enumerate(input_metadata.seq_groups):
         seq_ids, sampling_params = seq_group
         temperature = sampling_params.temperature
-        if temperature == 0.0:
+        if temperature < _SAMPLING_EPS:
             # NOTE: Zero temperature means deterministic sampling
             # (i.e., greedy sampling or beam search).
             # Set the temperature to 1 to avoid division by zero.
@@ -286,7 +287,7 @@ def _sample_from_prompt(
         beam_width = sampling_params.best_of
         _, next_token_ids = torch.topk(prob, beam_width)
         next_token_ids = next_token_ids.tolist()
-    elif sampling_params.temperature == 0.0:
+    elif sampling_params.temperature < _SAMPLING_EPS:
         # Greedy sampling.
         assert sampling_params.best_of == 1
         next_token_id = torch.argmax(prob)
@@ -343,7 +344,7 @@ def _sample_from_generation_tokens(
 
         parent_seq_ids = [beam_outputs[seq_id][0] for seq_id in seq_ids]
         next_token_ids = [beam_outputs[seq_id][1] for seq_id in seq_ids]
-    elif sampling_params.temperature == 0.0:
+    elif sampling_params.temperature < _SAMPLING_EPS:
         # Greedy sampling.
         assert len(seq_ids) == 1
         next_token_id = torch.argmax(probs, dim=-1)

vllm/sampling_params.py

@@ -1,6 +1,7 @@
 """Sampling parameters for text generation."""
 from typing import List, Optional, Union
 
+_SAMPLING_EPS = 1e-5
 
 class SamplingParams:
     """Sampling parameters for text generation.
@@ -71,7 +72,7 @@ def __init__(
         self._verify_args()
         if self.use_beam_search:
             self._verity_beam_search()
-        elif self.temperature == 0.0:
+        elif self.temperature < _SAMPLING_EPS:
             # Zero temperature means greedy sampling.
             self._verify_greedy_sampling()
 
@@ -106,9 +107,9 @@ def _verity_beam_search(self) -> None:
         if self.best_of == 1:
             raise ValueError("best_of must be greater than 1 when using beam "
                              f"search. Got {self.best_of}.")
-        if self.temperature > 0.0:
+        if self.temperature > _SAMPLING_EPS:
             raise ValueError("temperature must be 0 when using beam search.")
-        if self.top_p < 1.0:
+        if self.top_p < 1.0 - _SAMPLING_EPS:
             raise ValueError("top_p must be 1 when using beam search.")
         if self.top_k != -1:
             raise ValueError("top_k must be -1 when using beam search.")
@@ -117,7 +118,7 @@ def _verify_greedy_sampling(self) -> None:
         if self.best_of > 1:
             raise ValueError("best_of must be 1 when using greedy sampling."
                              f"Got {self.best_of}.")
-        if self.top_p < 1.0:
+        if self.top_p < 1.0 - _SAMPLING_EPS:
             raise ValueError("top_p must be 1 when using greedy sampling.")
         if self.top_k != -1:
             raise ValueError("top_k must be -1 when using greedy sampling.")