Add basic FP8 KV cache support (#2603)

* Add basic FP8 KV cache support

This change adds rudimentary FP8 KV cache support. The support is
enabled by passing `--kv-cache-dtype fp8_e5m2` to the launcher. Doing so
uses this type for the KV cache. However support is still limited:

* Only the `fp8_e5m2` type is supported.
* The KV cache layout is the same as `float16`/`bfloat16` (HND).
* The FP8 KV cache is only supported for FlashInfer.
* Loading of scales is not yet supported.

* Fix Cargo.toml

docs/source/reference/launcher.md

@@ -89,6 +89,15 @@ Options:
           [env: DTYPE=]
           [possible values: float16, bfloat16]
 
+```
+## KV_CACHE_DTYPE
+```shell
+      --kv-cache-dtype <KV_CACHE_DTYPE>
+          Specify the dtype for the key-value cache. When this option is not provided, the dtype of the model is used (typically `float16` or `bfloat16`). Currently the only supported value is `fp8_e5m2` on CUDA
+
+          [env: KV_CACHE_DTYPE=]
+          [possible values: fp8_e5m2]
+
 ```
 ## TRUST_REMOTE_CODE
 ```shell

integration-tests/conftest.py

@@ -336,6 +336,7 @@ def local_launcher(
         use_flash_attention: bool = True,
         disable_grammar_support: bool = False,
         dtype: Optional[str] = None,
+        kv_cache_dtype: Optional[str] = None,
         revision: Optional[str] = None,
         max_input_length: Optional[int] = None,
         max_batch_prefill_tokens: Optional[int] = None,
@@ -375,6 +376,9 @@ def local_launcher(
         if dtype is not None:
             args.append("--dtype")
             args.append(dtype)
+        if kv_cache_dtype is not None:
+            args.append("--kv-cache-dtype")
+            args.append(kv_cache_dtype)
         if revision is not None:
             args.append("--revision")
             args.append(revision)
@@ -434,6 +438,7 @@ def docker_launcher(
         use_flash_attention: bool = True,
         disable_grammar_support: bool = False,
         dtype: Optional[str] = None,
+        kv_cache_dtype: Optional[str] = None,
         revision: Optional[str] = None,
         max_input_length: Optional[int] = None,
         max_batch_prefill_tokens: Optional[int] = None,
@@ -456,6 +461,9 @@ def docker_launcher(
         if dtype is not None:
             args.append("--dtype")
             args.append(dtype)
+        if kv_cache_dtype is not None:
+            args.append("--kv-cache-dtype")
+            args.append(kv_cache_dtype)
         if revision is not None:
             args.append("--revision")
             args.append(revision)
@@ -589,7 +597,6 @@ async def generate_load_inner(
         max_new_tokens: int,
         seed: Optional[int] = None,
     ) -> List[Response]:
-
         import numpy as np
 
         arange = np.arange(len(prompts))

integration-tests/models/__snapshots__/test_flash_llama_fp8_kv_cache/test_flash_llama_fp8_kv_cache.json

@@ -0,0 +1,104 @@
+{
+  "details": {
+    "best_of_sequences": null,
+    "finish_reason": "length",
+    "generated_tokens": 10,
+    "prefill": [
+      {
+        "id": 128000,
+        "logprob": null,
+        "text": "<|begin_of_text|>"
+      },
+      {
+        "id": 3923,
+        "logprob": -5.6328125,
+        "text": "What"
+      },
+      {
+        "id": 374,
+        "logprob": -1.2265625,
+        "text": " is"
+      },
+      {
+        "id": 5655,
+        "logprob": -9.1015625,
+        "text": " deep"
+      },
+      {
+        "id": 6975,
+        "logprob": -1.8085938,
+        "text": " learning"
+      },
+      {
+        "id": 30,
+        "logprob": -1.0439453,
+        "text": "?"
+      }
+    ],
+    "seed": null,
+    "tokens": [
+      {
+        "id": 18682,
+        "logprob": -2.1992188,
+        "special": false,
+        "text": " Deep"
+      },
+      {
+        "id": 6975,
+        "logprob": -0.079956055,
+        "special": false,
+        "text": " learning"
+      },
+      {
+        "id": 374,
+        "logprob": -0.2763672,
+        "special": false,
+        "text": " is"
+      },
+      {
+        "id": 264,
+        "logprob": -0.37548828,
+        "special": false,
+        "text": " a"
+      },
+      {
+        "id": 27084,
+        "logprob": -1.4628906,
+        "special": false,
+        "text": " subset"
+      },
+      {
+        "id": 315,
+        "logprob": -0.02885437,
+        "special": false,
+        "text": " of"
+      },
+      {
+        "id": 5780,
+        "logprob": -0.2565918,
+        "special": false,
+        "text": " machine"
+      },
+      {
+        "id": 6975,
+        "logprob": -0.0063438416,
+        "special": false,
+        "text": " learning"
+      },
+      {
+        "id": 430,
+        "logprob": -1.3056641,
+        "special": false,
+        "text": " that"
+      },
+      {
+        "id": 374,
+        "logprob": -1.6035156,
+        "special": false,
+        "text": " is"
+      }
+    ],
+    "top_tokens": null
+  },
+  "generated_text": " Deep learning is a subset of machine learning that is"
+}

integration-tests/models/__snapshots__/test_flash_llama_fp8_kv_cache/test_flash_llama_fp8_kv_cache_all_params.json

@@ -0,0 +1,57 @@
+{
+  "details": {
+    "best_of_sequences": null,
+    "finish_reason": "eos_token",
+    "generated_tokens": 3,
+    "prefill": [
+      {
+        "id": 128000,
+        "logprob": null,
+        "text": "<|begin_of_text|>"
+      },
+      {
+        "id": 374,
+        "logprob": -22.96875,
+        "text": " is"
+      },
+      {
+        "id": 5655,
+        "logprob": -10.71875,
+        "text": " deep"
+      },
+      {
+        "id": 6975,
+        "logprob": -2.6992188,
+        "text": " learning"
+      },
+      {
+        "id": 30,
+        "logprob": -4.8398438,
+        "text": "?"
+      }
+    ],
+    "seed": 0,
+    "tokens": [
+      {
+        "id": 720,
+        "logprob": -0.4411621,
+        "special": false,
+        "text": " \n"
+      },
+      {
+        "id": 220,
+        "logprob": -0.35864258,
+        "special": false,
+        "text": " "
+      },
+      {
+        "id": 128001,
+        "logprob": 0.0,
+        "special": true,
+        "text": "<|end_of_text|>"
+      }
+    ],
+    "top_tokens": null
+  },
+  "generated_text": "What is deep learning? \n "
+}