model.py

# SPDX-FileCopyrightText: Copyright (c) 2022-2023 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from tensorrt_llm.models.llama.model import LLaMAForCausalLM

from ..._common import default_net
from ..._utils import pad_vocab_size
from ...functional import ACT2FN, stack
from ...layers import ColumnLinear
from ...mapping import Mapping
from ...module import Module, ModuleList


class MedusaLayer(Module):

    def __init__(
            self,
            hidden_size,
            hidden_act="silu",
            dtype=None,
            mapping=Mapping(),
    ):
        super().__init__()
        self.linear = ColumnLinear(hidden_size,
                                   hidden_size,
                                   dtype=dtype,
                                   tp_group=mapping.tp_group,
                                   tp_size=mapping.tp_size,
                                   gather_output=True)
        self.hidden_act = hidden_act

    def forward(self, x):
        return x + ACT2FN[self.hidden_act](self.linear(x))


class MedusaHead(Module):

    def __init__(
            self,
            num_layers,
            hidden_size,
            vocab_size,
            hidden_act="silu",
            dtype=None,
            mapping=Mapping(),
    ):
        super().__init__()
        self.medusa_layers = ModuleList([
            MedusaLayer(hidden_size=hidden_size,
                        hidden_act=hidden_act,
                        dtype=dtype,
                        mapping=mapping) for _ in range(num_layers)
        ])
        self.lm_head = ColumnLinear(hidden_size,
                                    vocab_size,
                                    bias=False,
                                    dtype=dtype,
                                    tp_group=mapping.tp_group,
                                    tp_size=mapping.tp_size,
                                    gather_output=True)
        return

    def forward(self, x):
        hidden_states = x
        for layer in self.medusa_layers:
            hidden_states = layer(hidden_states)
        return self.lm_head(hidden_states)


class MedusaForCausalLm(LLaMAForCausalLM):

    def __init__(self, config):

        super().__init__(config)
        self.num_medusa_heads = config.num_medusa_heads
        self.num_medusa_layers = config.num_medusa_layers
        self.hidden_size = config.hidden_size
        self.vocab_size = config.vocab_size
        vocab_size_padded = pad_vocab_size(self.vocab_size,
                                           config.mapping.tp_size)
        self.medusa_heads = ModuleList([
            MedusaHead(num_layers=self.num_medusa_layers,
                       hidden_size=config.hidden_size,
                       vocab_size=vocab_size_padded,
                       hidden_act=config.hidden_act,
                       dtype=config.dtype,
                       mapping=config.mapping)
            for _ in range(self.num_medusa_heads)
        ])
        self.max_medusa_token_len = config.max_draft_len

    def forward(self, *args, **kwargs):
        output_original = True
        hidden_states = super().forward(*args, **kwargs)

        if kwargs['use_cache']:
            if default_net().plugin_config.paged_kv_cache:
                lm_logits, hidden_states = hidden_states
            else:
                lm_logits, presents, hidden_states = hidden_states

        if self.mapping.is_last_pp_rank():
            medusa_logits = []
            for i in range(self.num_medusa_heads):
                medusa_logits.append(self.medusa_heads[i](hidden_states))
            # [num_medusa_heads, batch_size, num_medusa_tokens + 1, padded_vocab_size].
            # Remove padding [num_medusa_heads, batch_size * num_medusa_tokens + 1, padded_vocab_size].
            medusa_logits = stack(medusa_logits, dim=0)
            medusa_logits.mark_output('medusa_logits', self.config.logits_dtype)
        else:
            hidden_states.mark_output('hidden_states_output', self.config.dtype)

        if kwargs['use_cache'] and default_net(
        ).plugin_config.paged_kv_cache == False:
            if self.mapping.is_last_pp_rank():
                if output_original:
                    return (medusa_logits, lm_logits, presents)
                return (medusa_logits, presents)
            return (hidden_states, presents)
        else:
            if self.mapping.is_last_pp_rank():
                if output_original:
                    return medusa_logits, lm_logits
                return medusa_logits
            return hidden_states

    def prepare_inputs(self, *args, **kwargs):
        kwargs['speculative_decoding_draft_tokens_external'] = False
        kwargs['max_draft_len'] = self.max_medusa_token_len
        return super().prepare_inputs(*args, **kwargs)