77 lines
3.4 KiB
Python
77 lines
3.4 KiB
Python
import torch
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from vllm.model_executor.layers.quantization.base_config import (
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QuantizationConfig, QuantizeMethodBase)
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from vllm.utils import print_warning_once
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class BaseKVCacheMethod(QuantizeMethodBase):
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"""
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Quant method that adds `_k_scale` and `_v_scale` attributes to the
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Attention layer to support loading those scaling factors from checkpoints.
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The k/v_scale will be used to:
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- quantize k/v_cache entries before saving them to the cache
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- dequantize k/v_cache entries before fetching them from the cache
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:param quant_config: the appropriate QuantizationConfig
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"""
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def __init__(self, quant_config: QuantizationConfig):
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self.quant_config = quant_config
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def create_weights(self, layer: torch.nn.Module):
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"""
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Create "weight" (aka k_scale and v_scale) for an attention layer.
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"""
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# Initialize the KV cache scales to -1.0, which is an invalid value.
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# If the k/v_scale appears in the checkpoint, it will be
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# overwritten when loading weights.
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layer.k_scale = torch.nn.Parameter(torch.tensor(-1.0),
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requires_grad=False)
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layer.v_scale = torch.nn.Parameter(torch.tensor(-1.0),
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requires_grad=False)
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def apply(self, layer: torch.nn.Module) -> torch.Tensor:
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raise RuntimeError(
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f"{self.__class__.__name__}.apply should not be called.")
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def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
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# If the kv-cache dtype is auto, we enforce the k/v_scale to be 1.0
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# regardless whether the kv-scale is available in the checkpoint.
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if layer.kv_cache_dtype != "auto":
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if layer.k_scale > 0.0 and layer.v_scale > 0.0:
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# We prefer to use separate k_scale and v_scale if present
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k_scale = layer.k_scale.to("cpu").tolist()
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v_scale = layer.v_scale.to("cpu").tolist()
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elif layer.k_scale < 0.0 and layer.v_scale < 0.0:
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# If no scales were loaded (both scales are invalid negative
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# values), use the default value of 1.0
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k_scale = 1.0
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v_scale = 1.0
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else:
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# If we find a single kv_scale in the checkpoint, we remap
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# kv_scale to k_scale during weight loading, and duplicate
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# k_scale to v_scale here
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assert layer.k_scale > 0.0
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scale_to_duplicate = max(layer.k_scale, layer.v_scale)
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k_scale = scale_to_duplicate.to("cpu").tolist()
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v_scale = scale_to_duplicate.to("cpu").tolist()
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if not isinstance(k_scale, float) or not isinstance(
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v_scale, float):
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raise ValueError("Only support per-tensor scaling factor "
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"for fp8 KV cache")
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# These are used in the final Attention.forward()
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layer._k_scale = k_scale
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layer._v_scale = v_scale
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if (layer._k_scale == 1.0 and layer._v_scale == 1.0
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and "e5m2" not in layer.kv_cache_dtype):
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print_warning_once(
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"Using KV cache scaling factor 1.0 for fp8_e4m3. This "
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"may cause accuracy issues. Please make sure k/v_scale "
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"scaling factors are available in the fp8 checkpoint.")
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del layer.k_scale
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del layer.v_scale
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