weight_utils.py

# Adapted from https://github.com/vllm-project/vllm/blob/v0.6.4.post1/vllm/model_executor/model_loader/weight_utils.py

"""Utilities for downloading and initializing model weights."""
import fnmatch
import glob
import hashlib
import json
import logging
import os
import tempfile
from collections import defaultdict
from typing import (
    Any,
    Callable,
    Dict,
    Generator,
    Iterable,
    List,
    Optional,
    Tuple,
    Union,
)

import filelock
import gguf
import huggingface_hub.constants
import numpy as np
import torch
from huggingface_hub import HfFileSystem, hf_hub_download, snapshot_download
from pydantic import BaseModel, ConfigDict, ValidationInfo, model_validator
from safetensors.torch import load_file, safe_open, save_file
from tqdm.auto import tqdm

from sglang.srt.configs.load_config import LoadConfig
from sglang.srt.configs.model_config import ModelConfig
from sglang.srt.distributed import get_tensor_model_parallel_rank
from sglang.srt.layers.quantization import QuantizationConfig, get_quantization_config
from sglang.srt.utils import print_warning_once

logger = logging.getLogger(__name__)

# use system-level temp directory for file locks, so that multiple users
# can share the same lock without error.
# lock files in the temp directory will be automatically deleted when the
# system reboots, so users will not complain about annoying lock files
temp_dir = tempfile.gettempdir()


def enable_hf_transfer():
    """automatically activates hf_transfer"""
    if "HF_HUB_ENABLE_HF_TRANSFER" not in os.environ:
        try:
            # enable hf hub transfer if available
            import hf_transfer  # type: ignore # noqa

            huggingface_hub.constants.HF_HUB_ENABLE_HF_TRANSFER = True
        except ImportError:
            pass


enable_hf_transfer()


class DisabledTqdm(tqdm):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs, disable=True)


def get_lock(model_name_or_path: str, cache_dir: Optional[str] = None):
    lock_dir = cache_dir or temp_dir
    os.makedirs(os.path.dirname(lock_dir), exist_ok=True)
    model_name = model_name_or_path.replace("/", "-")
    hash_name = hashlib.sha256(model_name.encode()).hexdigest()
    # add hash to avoid conflict with old users' lock files
    lock_file_name = hash_name + model_name + ".lock"
    # mode 0o666 is required for the filelock to be shared across users
    lock = filelock.FileLock(os.path.join(lock_dir, lock_file_name), mode=0o666)
    return lock


def _shared_pointers(tensors):
    ptrs = defaultdict(list)
    for k, v in tensors.items():
        ptrs[v.data_ptr()].append(k)
    failing = []
    for _, names in ptrs.items():
        if len(names) > 1:
            failing.append(names)
    return failing


def convert_bin_to_safetensor_file(
    pt_filename: str,
    sf_filename: str,
) -> None:
    loaded = torch.load(pt_filename, map_location="cpu")
    if "state_dict" in loaded:
        loaded = loaded["state_dict"]
    shared = _shared_pointers(loaded)
    for shared_weights in shared:
        for name in shared_weights[1:]:
            loaded.pop(name)

    # For tensors to be contiguous
    loaded = {k: v.contiguous() for k, v in loaded.items()}

    dirname = os.path.dirname(sf_filename)
    os.makedirs(dirname, exist_ok=True)
    save_file(loaded, sf_filename, metadata={"format": "pt"})

    # check file size
    sf_size = os.stat(sf_filename).st_size
    pt_size = os.stat(pt_filename).st_size
    if (sf_size - pt_size) / pt_size > 0.01:
        raise RuntimeError(
            f"""The file size different is more than 1%:
         - {sf_filename}: {sf_size}
         - {pt_filename}: {pt_size}
         """
        )

    # check if the tensors are the same
    reloaded = load_file(sf_filename)
    for k in loaded:
        pt_tensor = loaded[k]
        sf_tensor = reloaded[k]
        if not torch.equal(pt_tensor, sf_tensor):
            raise RuntimeError(f"The output tensors do not match for key {k}")


# TODO(woosuk): Move this to other place.
def get_quant_config(
    model_config: ModelConfig, load_config: LoadConfig
) -> QuantizationConfig:

    quant_cls = get_quantization_config(model_config.quantization)

    # GGUF doesn't have config file
    if model_config.quantization == "gguf":
        return quant_cls.from_config({})

    # Read the quantization config from the HF model config, if available.
    hf_quant_config = getattr(model_config.hf_config, "quantization_config", None)
    # some vision model may keep quantization_config in their text_config
    hf_text_config = getattr(model_config.hf_config, "text_config", None)
    if hf_quant_config is None and hf_text_config is not None:
        hf_quant_config = getattr(hf_text_config, "quantization_config", None)
    if hf_quant_config is None:
        # compressed-tensors uses a compressions_config
        hf_quant_config = getattr(model_config.hf_config, "compression_config", None)
    if hf_quant_config is not None:
        return quant_cls.from_config(hf_quant_config)
    # In case of bitsandbytes/QLoRA, get quant config from the adapter model.
    if model_config.quantization == "bitsandbytes":
        if (
            not load_config.model_loader_extra_config
            or "qlora_adapter_name_or_path" not in load_config.model_loader_extra_config
        ):
            return quant_cls.from_config({"adapter_name_or_path": ""})
        model_name_or_path = load_config.model_loader_extra_config[
            "qlora_adapter_name_or_path"
        ]

    else:
        model_name_or_path = model_config.model_path
    is_local = os.path.isdir(model_name_or_path)
    if not is_local:
        # Download the config files.
        with get_lock(model_name_or_path, load_config.download_dir):
            hf_folder = snapshot_download(
                model_name_or_path,
                revision=model_config.revision,
                allow_patterns="*.json",
                cache_dir=load_config.download_dir,
                local_files_only=huggingface_hub.constants.HF_HUB_OFFLINE,
                tqdm_class=DisabledTqdm,
            )
    else:
        hf_folder = model_name_or_path

    possible_config_filenames = quant_cls.get_config_filenames()

    # If the quantization config is not found, use the default config.
    if not possible_config_filenames:
        return quant_cls()

    config_files = glob.glob(os.path.join(hf_folder, "*.json"))

    quant_config_files = [
        f for f in config_files if any(f.endswith(x) for x in possible_config_filenames)
    ]
    if len(quant_config_files) == 0:
        raise ValueError(f"Cannot find the config file for {model_config.quantization}")
    if len(quant_config_files) > 1:
        raise ValueError(
            f"Found multiple config files for {model_config.quantization}: "
            f"{quant_config_files}"
        )

    quant_config_file = quant_config_files[0]
    with open(quant_config_file) as f:
        config = json.load(f)

        if model_config.quantization == "bitsandbytes":
            config["adapter_name_or_path"] = model_name_or_path
        elif model_config.quantization == "modelopt":
            if config["producer"]["name"] == "modelopt":
                return quant_cls.from_config(config)
            else:
                raise ValueError(
                    f"Unsupported quantization config"
                    f" found for {model_config.quantization} in {f}."
                )

    return quant_cls.from_config(config)


def download_weights_from_hf(
    model_name_or_path: str,
    cache_dir: Optional[str],
    allow_patterns: List[str],
    revision: Optional[str] = None,
    ignore_patterns: Optional[Union[str, List[str]]] = None,
) -> str:
    """Download model weights from Hugging Face Hub.

    Args:
        model_name_or_path (str): The model name or path.
        cache_dir (Optional[str]): The cache directory to store the model
            weights. If None, will use HF defaults.
        allow_patterns (List[str]): The allowed patterns for the
            weight files. Files matched by any of the patterns will be
            downloaded.
        revision (Optional[str]): The revision of the model.
        ignore_patterns (Optional[Union[str, List[str]]]): The patterns to
            filter out the weight files. Files matched by any of the patterns
            will be ignored.

    Returns:
        str: The path to the downloaded model weights.
    """
    if not huggingface_hub.constants.HF_HUB_OFFLINE:
        # Before we download we look at that is available:
        fs = HfFileSystem()
        file_list = fs.ls(model_name_or_path, detail=False, revision=revision)

        # depending on what is available we download different things
        for pattern in allow_patterns:
            matching = fnmatch.filter(file_list, pattern)
            if len(matching) > 0:
                allow_patterns = [pattern]
                break

    logger.info("Using model weights format %s", allow_patterns)
    # Use file lock to prevent multiple processes from
    # downloading the same model weights at the same time.
    with get_lock(model_name_or_path, cache_dir):
        hf_folder = snapshot_download(
            model_name_or_path,
            allow_patterns=allow_patterns,
            ignore_patterns=ignore_patterns,
            cache_dir=cache_dir,
            tqdm_class=DisabledTqdm,
            revision=revision,
            local_files_only=huggingface_hub.constants.HF_HUB_OFFLINE,
        )
    return hf_folder


def download_safetensors_index_file_from_hf(
    model_name_or_path: str,
    index_file: str,
    cache_dir: Optional[str],
    revision: Optional[str] = None,
) -> None:
    """Download hf safetensors index file from Hugging Face Hub.

    Args:
        model_name_or_path (str): The model name or path.
        cache_dir (Optional[str]): The cache directory to store the model
            weights. If None, will use HF defaults.
        revision (Optional[str]): The revision of the model.
    """
    # Use file lock to prevent multiple processes from
    # downloading the same model weights at the same time.
    with get_lock(model_name_or_path, cache_dir):
        try:
            # Download the safetensors index file.
            hf_hub_download(
                repo_id=model_name_or_path,
                filename=index_file,
                cache_dir=cache_dir,
                revision=revision,
                local_files_only=huggingface_hub.constants.HF_HUB_OFFLINE,
            )
        # If file not found on remote or locally, we should not fail since
        # only some models will have index_file.
        except huggingface_hub.utils.EntryNotFoundError:
            logger.info("No %s found in remote.", index_file)
        except huggingface_hub.utils.LocalEntryNotFoundError:
            logger.info("No %s found in local cache.", index_file)


# For models like Mistral-7B-v0.3, there are both sharded
# safetensors files and a consolidated safetensors file.
# Passing both of these to the weight loader functionality breaks.
# So, we use the index_file to
# look up which safetensors files should be used.
def filter_duplicate_safetensors_files(
    hf_weights_files: List[str], hf_folder: str, index_file: str
) -> List[str]:
    # model.safetensors.index.json is a mapping from keys in the
    # torch state_dict to safetensors file holding that weight.
    index_file_name = os.path.join(hf_folder, index_file)
    if not os.path.isfile(index_file_name):
        return hf_weights_files

    # Iterate through the weight_map (weight_name: safetensors files)
    # to identify weights that we should use.
    with open(index_file_name) as f:
        weight_map = json.load(f)["weight_map"]
    weight_files_in_index = set()
    for weight_name in weight_map:
        weight_files_in_index.add(os.path.join(hf_folder, weight_map[weight_name]))
    # Filter out any fields that are not found in the index file.
    hf_weights_files = [f for f in hf_weights_files if f in weight_files_in_index]
    return hf_weights_files


def filter_files_not_needed_for_inference(hf_weights_files: List[str]) -> List[str]:
    """
    Exclude files that are not needed for inference.

    See https://github.com/huggingface/transformers/blob/v4.34.0/src/transformers/trainer.py#L227-L233
    """
    blacklist = [
        "training_args.bin",
        "optimizer.bin",
        "optimizer.pt",
        "scheduler.pt",
        "scaler.pt",
    ]
    hf_weights_files = [
        f for f in hf_weights_files if not any(f.endswith(x) for x in blacklist)
    ]
    return hf_weights_files


# explicitly use pure text format, with a newline at the end
# this makes it impossible to see the animation in the progress bar
# but will avoid messing up with ray or multiprocessing, which wraps
# each line of output with some prefix.
_BAR_FORMAT = "{desc}: {percentage:3.0f}% Completed | {n_fmt}/{total_fmt} [{elapsed}<{remaining}, {rate_fmt}]\n"  # noqa: E501


def np_cache_weights_iterator(
    model_name_or_path: str,
    cache_dir: Optional[str],
    hf_folder: str,
    hf_weights_files: List[str],
) -> Generator[Tuple[str, torch.Tensor], None, None]:
    """Iterate over the weights in the model np files.

    Will dump the model weights to numpy files if they are not already dumped.
    """
    enable_tqdm = (
        not torch.distributed.is_initialized() or torch.distributed.get_rank() == 0
    )
    # Convert the model weights from torch tensors to numpy arrays for
    # faster loading.
    np_folder = os.path.join(hf_folder, "np")
    os.makedirs(np_folder, exist_ok=True)
    weight_names_file = os.path.join(np_folder, "weight_names.json")
    # Use file lock to prevent multiple processes from
    # dumping the same model weights to numpy at the same time.
    with get_lock(model_name_or_path, cache_dir):
        if not os.path.exists(weight_names_file):
            weight_names: List[str] = []
            for bin_file in tqdm(
                hf_weights_files,
                desc="Loading np_cache checkpoint shards",
                disable=not enable_tqdm,
                bar_format=_BAR_FORMAT,
            ):
                state = torch.load(bin_file, map_location="cpu")
                for name, param in state.items():
                    param_path = os.path.join(np_folder, name)
                    with open(param_path, "wb") as f:
                        np.save(f, param.cpu().detach().numpy())
                    weight_names.append(name)
            with open(weight_names_file, "w") as f:
                json.dump(weight_names, f)

    with open(weight_names_file) as f:
        weight_names = json.load(f)

    for name in weight_names:
        param_path = os.path.join(np_folder, name)
        with open(param_path, "rb") as f:
            param = np.load(f)
        yield name, torch.from_numpy(param)


def safetensors_weights_iterator(
    hf_weights_files: List[str],
    is_all_weights_sharded: bool = False,
) -> Generator[Tuple[str, torch.Tensor], None, None]:
    """Iterate over the weights in the model safetensor files.

    If is_all_weights_sharded is True, it uses more optimize read by reading an
    entire file instead of reading each tensor one by one.
    """
    enable_tqdm = (
        not torch.distributed.is_initialized() or torch.distributed.get_rank() == 0
    )
    for st_file in tqdm(
        hf_weights_files,
        desc="Loading safetensors checkpoint shards",
        disable=not enable_tqdm,
        bar_format=_BAR_FORMAT,
    ):
        if not is_all_weights_sharded:
            with safe_open(st_file, framework="pt") as f:
                for name in f.keys():  # noqa: SIM118
                    param = f.get_tensor(name)
                    yield name, param
        else:
            result = load_file(st_file, device="cpu")
            for name, param in result.items():
                yield name, param


def pt_weights_iterator(
    hf_weights_files: List[str],
) -> Generator[Tuple[str, torch.Tensor], None, None]:
    """Iterate over the weights in the model bin/pt files."""
    enable_tqdm = (
        not torch.distributed.is_initialized() or torch.distributed.get_rank() == 0
    )
    for bin_file in tqdm(
        hf_weights_files,
        desc="Loading pt checkpoint shards",
        disable=not enable_tqdm,
        bar_format=_BAR_FORMAT,
    ):
        state = torch.load(bin_file, map_location="cpu")
        yield from state.items()
        del state
        torch.cuda.empty_cache()


def get_gguf_extra_tensor_names(
    gguf_file: str, gguf_to_hf_name_map: Dict[str, str]
) -> List[str]:
    reader = gguf.GGUFReader(gguf_file)
    expected_gguf_keys = set(gguf_to_hf_name_map.keys())
    exact_gguf_keys = set([tensor.name for tensor in reader.tensors])
    extra_keys = expected_gguf_keys - exact_gguf_keys
    return [gguf_to_hf_name_map[key] for key in extra_keys]


def gguf_quant_weights_iterator(
    gguf_file: str, gguf_to_hf_name_map: Dict[str, str]
) -> Generator[Tuple[str, torch.Tensor], None, None]:
    """
    Iterate over the quant weights in the model gguf files and convert
    them to torch tensors
    """

    reader = gguf.GGUFReader(gguf_file)

    for tensor in reader.tensors:
        if tensor.name in gguf_to_hf_name_map:
            weight_type = tensor.tensor_type
            name = gguf_to_hf_name_map[tensor.name]

            if weight_type.name != "F32":
                weight_type_name = name.replace("weight", "qweight_type")
                weight_type = torch.tensor(weight_type)
                yield weight_type_name, weight_type

    for tensor in reader.tensors:
        if tensor.name in gguf_to_hf_name_map:
            weight = tensor.data
            weight_type = tensor.tensor_type
            name = gguf_to_hf_name_map[tensor.name]

            if weight_type.name != "F32":
                name = name.replace("weight", "qweight")
            param = torch.tensor(weight)
            yield name, param


def convert_pyslice_to_tensor(x: Any) -> torch.Tensor:
    """convert PySafeSlice object from safetensors to torch.Tensor

    PySafeSlice object supports indexing, which is done before loading the
    actual tensor and can reduce the amount of memory being read into the
    memory. However, it does not support more advanced functionalities
    like `.view()` or `.t()`. Therefore, if we need to modify the loaded
    tensor with these more complicated operators, we need to convert to
    tensor first.
    """
    if not isinstance(x, torch.Tensor):
        x = x[:]
    return x


def default_weight_loader(param: torch.Tensor, loaded_weight: torch.Tensor) -> None:
    """Default weight loader."""
    try:
        if param.numel() == 1 and loaded_weight.numel() == 1:
            # Sometimes scalar values aren't considered tensors with shapes
            # so if both param and loaded_weight are a scalar,
            # "broadcast" instead of copy
            param.data.fill_(loaded_weight.item())
        else:
            assert param.size() == loaded_weight.size(), (
                f"Attempted to load weight ({loaded_weight.size()}) "
                f"into parameter ({param.size()})"
            )

            param.data.copy_(loaded_weight)
    except Exception:
        # NOTE: This exception is added for the purpose of setting breakpoint to
        # debug weight loading issues.
        raise


def row_parallel_weight_loader(
    param: torch.Tensor, loaded_weight: torch.Tensor
) -> None:
    """Load weights that are row-parallelized."""
    tp_rank = get_tensor_model_parallel_rank()
    shard_dim = 0 if param.dim() != 1 else None

    if shard_dim is not None:
        shard_size = param.data.shape[shard_dim]
        start_idx = tp_rank * shard_size
        loaded_weight = loaded_weight.narrow(shard_dim, start_idx, shard_size)

    return default_weight_loader(param, loaded_weight)


LoaderFunction = Callable[[torch.Tensor, torch.Tensor], torch.Tensor]


def sharded_weight_loader(shard_axis: int) -> LoaderFunction:
    """Create a weight loader that shards the weights along the given axis"""

    def loader(param: torch.Tensor, loaded_weight: torch.Tensor) -> None:
        tp_rank = get_tensor_model_parallel_rank()

        shard_size = param.data.shape[shard_axis]
        start_idx = tp_rank * shard_size
        loaded_weight = loaded_weight.narrow(shard_axis, start_idx, shard_size)

        return default_weight_loader(param, loaded_weight)

    return loader


def composed_weight_loader(
    loader: LoaderFunction, fn: Callable[[torch.Tensor], torch.Tensor]
) -> LoaderFunction:
    """Create a weight loader that post-processes the weights after loading"""

    def composed_loader(param: torch.Tensor, loaded_weight: torch.Tensor) -> None:
        loader(param, loaded_weight)
        param.data.copy_(fn(param))
        return

    return composed_loader


def initialize_dummy_weights(
    model: torch.nn.Module,
    low: float = -1e-3,
    high: float = 1e-3,
    seed: int = 1234,
) -> None:
    """Initialize model weights with random values.

    The model weights must be randomly initialized for accurate performance
    measurements. Additionally, the model weights should not cause NaNs in the
    forward pass. We empirically found that initializing the weights with
    values between -1e-3 and 1e-3 works well for most models.

    We use per-parameter random seed, so that dummy weights are consistent,
    even if the model is partitioned across multiple devices. When the seed
    is fixed, the random values generated by this function only depends on
    the parameter's number of elements and its data type.
    """
    for param in model.state_dict().values():
        if torch.is_floating_point(param):
            generator = torch.Generator(device=param.data.device)
            generator.manual_seed(seed)
            if torch.finfo(param.data.dtype).bits < 16:
                # uniform_ doesn't support < 16-bit datatypes (FP8)
                dtype = param.data.dtype
                tmp_param = param.data.to(torch.float16)
                tmp_param = tmp_param.uniform_(low, high, generator=generator).to(dtype)
                param.data.copy_(tmp_param)
            else:
                param.uniform_(low, high, generator=generator)


def maybe_remap_kv_scale_name(name: str, params_dict: dict) -> Optional[str]:
    """Remap the name of FP8 k/v_scale parameters.

    This function handles the remapping of FP8 k/v_scale parameter names.
    It detects if the given name ends with a suffix and attempts to remap
    it to the expected name format in the model. If the remapped name is not
    found in the params_dict, a warning is printed and None is returned.

    Args:
        name (str): The original loaded checkpoint parameter name.
        params_dict (dict): Dictionary containing the model's named parameters.

    Returns:
        str: The remapped parameter name if successful, or the original name
             if no remapping is needed.
        None: If the remapped name is not found in params_dict.
    """
    if name.endswith(".kv_scale"):
        print_warning_once(
            "DEPRECATED. Found kv_scale in the checkpoint. "
            "This format is deprecated in favor of separate k_scale and "
            "v_scale tensors and will be removed in a future release. "
            "Functionally, we will remap kv_scale to k_scale and duplicate "
            "k_scale to v_scale"
        )
        # NOTE: we remap the deprecated kv_scale to k_scale
        remapped_name = name.replace(".kv_scale", ".attn.k_scale")
        if remapped_name not in params_dict:
            print_warning_once(
                f"Found kv_scale in the checkpoint (e.g. {name}), "
                "but not found the expected name in the model "
                f"(e.g. {remapped_name}). kv_scale is "
                "not loaded."
            )
            return None
        return remapped_name

    possible_scale_names = [".k_scale", ".v_scale"]
    for scale_name in possible_scale_names:
        if name.endswith(scale_name):
            remapped_name = name.replace(scale_name, f".attn{scale_name}")
            if remapped_name not in params_dict:
                print_warning_once(
                    f"Found {scale_name} in the checkpoint (e.g. {name}), "
                    "but not found the expected name in the model "
                    f"(e.g. {remapped_name}). {scale_name} is "
                    "not loaded."
                )
                return None
            return remapped_name

    # If there were no matches, return the untouched param name
    return name


# Adapted from https://github.com/vllm-project/vllm/blob/68ad4e3a8d8a66fb2a43be57471ee13a8bec4ec0/vllm/model_executor/layers/quantization/schema.py
class KVCacheQuantSchema(BaseModel):
    dtype: str
    # Each key is a TP rank. Each value is a dictionary mapping a TP rank's
    # layer indices to their per-tensor KV cache scaling factor.
    # TODO: Consider pulling this and its validation methods out into its
    # own schema class (tricky as its members are variable)
    scaling_factor: Dict[int, Dict[int, float]]

    @model_validator(mode="after")
    def check_is_fp8(self) -> "KVCacheQuantSchema":
        assert self.dtype == "float8_e4m3fn", (
            "Loaded scaling factors intended for KV cache dtype = "
            f"{self.dtype} rather than float8_e4m3fn!"
        )
        return self

    @model_validator(mode="after")
    def check_tp_ranks(self, info: ValidationInfo) -> "KVCacheQuantSchema":
        context = info.context
        if context:
            tp_size = context["tp_size"]
            num_hidden_layers = context["num_hidden_layers"]
            assert len(self.scaling_factor) == tp_size, (
                f"Loaded dictionary has TP size {len(self.scaling_factor)} "
                f"but LLM engine is currently running with TP size {tp_size}."
            )
            for tp_rank, layer_maps in self.scaling_factor.items():
                assert len(layer_maps) == num_hidden_layers, (
                    f"KV cache scales map for TP rank {tp_rank} is malformed. "
                    f"Expected {num_hidden_layers} layers, got "
                    f"{len(layer_maps)}."
                )
            for i in range(tp_size):
                assert (
                    i in self.scaling_factor
                ), f"KV cache scales map for TP rank {i} not found."
        return self

    @model_validator(mode="after")
    def check_current_rank(self, info: ValidationInfo) -> "KVCacheQuantSchema":
        context = info.context
        if context:
            tp_rank = context["tp_rank"]
            num_hidden_layers = context["num_hidden_layers"]
            layer_scales_map = self.scaling_factor[tp_rank]
            for i in range(num_hidden_layers):
                assert i in layer_scales_map, (
                    f"Could not find KV cache scales for layer {i} in "
                    f"TP rank {tp_rank}."
                )
        return self


class QuantParamSchema(BaseModel):
    # TODO: Generalize and extend with more fields
    # (e.g. weights/activations params) once functionality is enabled
    model_config = ConfigDict(protected_namespaces=())
    model_type: Optional[str]
    kv_cache: KVCacheQuantSchema

    @model_validator(mode="after")
    def check_model_type(self, info: ValidationInfo) -> "QuantParamSchema":
        context = info.context
        if context:
            model_type = context.get("model_type", None)
            if model_type is not None:
                assert model_type == self.model_type, (
                    f"Model type is {model_type} but loaded "
                    f"scaling factors belonging to different "
                    f"model type {self.model_type}!"
                )
        return self


def kv_cache_scales_loader(
    filename: str,
    tp_rank: int,
    tp_size: int,
    num_hidden_layers: int,
    model_type: Optional[str],
) -> Iterable[Tuple[int, float]]:
    """
    A simple utility to read in KV cache scaling factors that have been
    previously serialized to disk. Used by the model to populate the appropriate
    KV cache scaling factors. The serialization should represent a dictionary
    whose keys are the TP ranks and values are another dictionary mapping layers
    to their KV cache scaling factors.
    """
    try:
        with open(filename) as f:
            context = {
                "model_type": model_type,
                "num_hidden_layers": num_hidden_layers,
                "tp_rank": tp_rank,
                "tp_size": tp_size,
            }
            schema_dct = json.load(f)
            schema = QuantParamSchema.model_validate(schema_dct, context=context)
            layer_scales_map = schema.kv_cache.scaling_factor[tp_rank]
            return layer_scales_map.items()
    except FileNotFoundError:
        logger.error("File or directory '%s' not found.", filename)
    except json.JSONDecodeError:
        logger.error("Error decoding JSON in file '%s'.", filename)
    except Exception:
        logger.error("An error occurred while reading '%s'.", filename)
    # This section is reached if and only if any of the excepts are hit
    # Return an empty iterable (list) => no KV cache scales are loaded
    # which ultimately defaults to 1.0 scales
    logger.warning(
        "Defaulting to KV cache scaling factors = 1.0 for all "
        "layers in TP rank %d as an error occurred during loading.",
        tp_rank,
    )
    return []