Qwen MoE model. (#1960)

* Qwen MoE model.

* Add the MoE model to the example.

* Fix the scaling.

* Readme updates.

* Readme tweaks.

README.md

@@ -125,6 +125,8 @@ We also provide a some command line based examples using state of the art models
   [RepVGG](./candle-examples/examples/repvgg): computer vision models.
 - [BLIP](./candle-examples/examples/blip/): image to text model, can be used to
   generate captions for an image.
+- [CLIP](./candle-examples/examples/clip/): multi-model vision and language
+  model.
 - [TrOCR](./candle-examples/examples/trocr/): a transformer OCR model, with
   dedicated submodels for hand-writing and printed recognition.
 - [Marian-MT](./candle-examples/examples/marian-mt/): neural machine translation
@@ -206,7 +208,7 @@ If you have an addition to this list, please submit a pull request.
         - Replit-code-v1.5-3B.
         - Bert.
         - Yi-6B and Yi-34B.
-        - Qwen1.5.
+        - Qwen1.5, Qwen1.5 MoE.
         - RWKV v5 and v6.
     - Quantized LLMs.
         - Llama 7b, 13b, 70b, as well as the chat and code variants.

candle-examples/examples/qwen/README.md

@@ -0,0 +1,27 @@
+# candle-qwen: large language model series from Alibaba Cloud
+
+Qwen 1.5 is a series of large language models that provide strong performances
+on English and Chinese.
+
+- [Blog post](https://qwenlm.github.io/blog/qwen1.5/) introducing Qwen1.5.
+- [Model card](https://huggingface.co/Qwen/Qwen1.5-0.5B) on the HuggingFace Hub.
+- [Blog post](https://qwenlm.github.io/blog/qwen-moe/) for the
+  mixture-of-experts (MoE) variant.
+
+## Running the example
+
+```bash
+$ cargo run --example qwen --release  -- --prompt "Hello there "
+```
+
+Various model sizes are available via the `--model` argument, including the MoE
+variant.
+
+```bash
+$ cargo run --example qwen --release  -- --prompt "Hello there " --model moe-a2.7b --prompt 'def print_prime(n: int): '
+def print_prime(n: int):  # n is the number of primes to be printed
+    for i in range(2, n + 1):
+        if all(i % j != 0 for j in range(2, i)):
+            print(i)
+```
+

candle-examples/examples/qwen/main.rs

@@ -7,7 +7,8 @@ extern crate accelerate_src;
 use anyhow::{Error as E, Result};
 use clap::Parser;
 
-use candle_transformers::models::qwen2::{Config, Model};
+use candle_transformers::models::qwen2::{Config as ConfigBase, Model as ModelBase};
+use candle_transformers::models::qwen2_moe::{Config as ConfigMoe, Model as ModelMoe};
 
 use candle::{DType, Device, Tensor};
 use candle_examples::token_output_stream::TokenOutputStream;
@@ -16,6 +17,20 @@ use candle_transformers::generation::LogitsProcessor;
 use hf_hub::{api::sync::Api, Repo, RepoType};
 use tokenizers::Tokenizer;
 
+enum Model {
+    Base(ModelBase),
+    Moe(ModelMoe),
+}
+
+impl Model {
+    fn forward(&mut self, xs: &Tensor, s: usize) -> candle::Result<Tensor> {
+        match self {
+            Self::Moe(ref mut m) => m.forward(xs, s),
+            Self::Base(ref mut m) => m.forward(xs, s),
+        }
+    }
+}
+
 struct TextGeneration {
     model: Model,
     device: Device,
@@ -127,6 +142,8 @@ enum WhichModel {
     W14b,
     #[value(name = "72b")]
     W72b,
+    #[value(name = "moe-a2.7b")]
+    MoeA27b,
 }
 
 #[derive(Parser, Debug)]
@@ -224,6 +241,7 @@ fn main() -> Result<()> {
                 WhichModel::W7b => "7B",
                 WhichModel::W14b => "14B",
                 WhichModel::W72b => "72B",
+                WhichModel::MoeA27b => "MoE-A2.7B",
             };
             format!("Qwen/Qwen1.5-{size}")
         }
@@ -244,7 +262,11 @@ fn main() -> Result<()> {
             .collect::<Vec<_>>(),
         None => match args.model {
             WhichModel::W0_5b | WhichModel::W1_8b => vec![repo.get("model.safetensors")?],
-            WhichModel::W4b | WhichModel::W7b | WhichModel::W14b | WhichModel::W72b => {
+            WhichModel::W4b
+            | WhichModel::W7b
+            | WhichModel::W14b
+            | WhichModel::W72b
+            | WhichModel::MoeA27b => {
                 candle_examples::hub_load_safetensors(&repo, "model.safetensors.index.json")?
             }
         },
@@ -254,7 +276,6 @@ fn main() -> Result<()> {
 
     let start = std::time::Instant::now();
     let config_file = repo.get("config.json")?;
-    let config: Config = serde_json::from_slice(&std::fs::read(config_file)?)?;
     let device = candle_examples::device(args.cpu)?;
     let dtype = if device.is_cuda() {
         DType::BF16
@@ -262,7 +283,16 @@ fn main() -> Result<()> {
         DType::F32
     };
     let vb = unsafe { VarBuilder::from_mmaped_safetensors(&filenames, dtype, &device)? };
-    let model = Model::new(&config, vb)?;
+    let model = match args.model {
+        WhichModel::MoeA27b => {
+            let config: ConfigMoe = serde_json::from_slice(&std::fs::read(config_file)?)?;
+            Model::Moe(ModelMoe::new(&config, vb)?)
+        }
+        _ => {
+            let config: ConfigBase = serde_json::from_slice(&std::fs::read(config_file)?)?;
+            Model::Base(ModelBase::new(&config, vb)?)
+        }
+    };
 
     println!("loaded the model in {:?}", start.elapsed());
 

candle-transformers/src/models/mod.rs

@@ -40,6 +40,7 @@ pub mod quantized_rwkv_v6;
 pub mod quantized_stable_lm;
 pub mod quantized_t5;
 pub mod qwen2;
+pub mod qwen2_moe;
 pub mod repvgg;
 pub mod resnet;
 pub mod rwkv_v5;

candle-transformers/src/models/qwen2_moe.rs

@@ -0,0 +1,488 @@
+use crate::models::with_tracing::{linear, linear_no_bias, Linear, RmsNorm};
+use candle::{DType, Device, Module, Result, Tensor, D};
+use candle_nn::{Activation, VarBuilder};
+use std::sync::Arc;
+
+#[derive(Debug, Clone, PartialEq, serde::Deserialize)]
+pub struct Config {
+    pub vocab_size: usize,
+    pub hidden_size: usize,
+    pub intermediate_size: usize,
+    pub num_hidden_layers: usize,
+    pub num_attention_heads: usize,
+    pub num_key_value_heads: usize,
+    pub max_position_embeddings: usize,
+    pub sliding_window: usize,
+    pub max_window_layers: usize,
+    pub tie_word_embeddings: bool,
+    pub rope_theta: f64,
+    pub rms_norm_eps: f64,
+    pub use_sliding_window: bool,
+    pub hidden_act: Activation,
+    pub decoder_sparse_step: usize,
+    pub moe_intermediate_size: usize,
+    pub shared_expert_intermediate_size: usize,
+    pub num_experts_per_tok: usize,
+    pub num_experts: usize,
+    pub norm_topk_prob: bool,
+}
+
+#[derive(Debug, Clone)]
+struct RotaryEmbedding {
+    sin: Tensor,
+    cos: Tensor,
+}
+
+fn rotate_half(xs: &Tensor) -> Result<Tensor> {
+    let last_dim = xs.dim(D::Minus1)?;
+    let xs1 = xs.narrow(D::Minus1, 0, last_dim / 2)?;
+    let xs2 = xs.narrow(D::Minus1, last_dim / 2, last_dim - last_dim / 2)?;
+    Tensor::cat(&[&xs2.neg()?, &xs1], D::Minus1)
+}
+
+impl RotaryEmbedding {
+    fn new(dtype: DType, cfg: &Config, dev: &Device) -> Result<Self> {
+        let dim = cfg.hidden_size / cfg.num_attention_heads;
+        let max_seq_len = cfg.max_position_embeddings;
+        let inv_freq: Vec<_> = (0..dim)
+            .step_by(2)
+            .map(|i| 1f32 / cfg.rope_theta.powf(i as f64 / dim as f64) as f32)
+            .collect();
+        let inv_freq_len = inv_freq.len();
+        let inv_freq = Tensor::from_vec(inv_freq, (1, inv_freq_len), dev)?.to_dtype(dtype)?;
+        let t = Tensor::arange(0u32, max_seq_len as u32, dev)?
+            .to_dtype(dtype)?
+            .reshape((max_seq_len, 1))?;
+        let freqs = t.matmul(&inv_freq)?;
+        let freqs = Tensor::cat(&[&freqs, &freqs], D::Minus1)?;
+        Ok(Self {
+            sin: freqs.sin()?,
+            cos: freqs.cos()?,
+        })
+    }
+
+    fn apply_rotary_emb_qkv(
+        &self,
+        q: &Tensor,
+        k: &Tensor,
+        seqlen_offset: usize,
+    ) -> Result<(Tensor, Tensor)> {
+        let (_b_sz, _h, seq_len, _n_embd) = q.dims4()?;
+        let cos = self.cos.narrow(0, seqlen_offset, seq_len)?;
+        let sin = self.sin.narrow(0, seqlen_offset, seq_len)?;
+        let cos = cos.unsqueeze(0)?.unsqueeze(0)?; // (1, 1, seq_len, dim)
+        let sin = sin.unsqueeze(0)?.unsqueeze(0)?; // (1, 1, seq_len, dim)
+        let q_embed = (q.broadcast_mul(&cos)? + rotate_half(q)?.broadcast_mul(&sin))?;
+        let k_embed = (k.broadcast_mul(&cos)? + rotate_half(k)?.broadcast_mul(&sin))?;
+        Ok((q_embed, k_embed))
+    }
+}
+
+#[derive(Debug, Clone)]
+#[allow(clippy::upper_case_acronyms)]
+struct MLP {
+    gate_proj: Linear,
+    up_proj: Linear,
+    down_proj: Linear,
+    act_fn: Activation,
+}
+
+impl MLP {
+    fn new(intermediate_sz: usize, cfg: &Config, vb: VarBuilder) -> Result<Self> {
+        let hidden_sz = cfg.hidden_size;
+        let gate_proj = linear_no_bias(hidden_sz, intermediate_sz, vb.pp("gate_proj"))?;
+        let up_proj = linear_no_bias(hidden_sz, intermediate_sz, vb.pp("up_proj"))?;
+        let down_proj = linear_no_bias(intermediate_sz, hidden_sz, vb.pp("down_proj"))?;
+        Ok(Self {
+            gate_proj,
+            up_proj,
+            down_proj,
+            act_fn: cfg.hidden_act,
+        })
+    }
+}
+
+impl Module for MLP {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        let lhs = xs.apply(&self.gate_proj)?.apply(&self.act_fn)?;
+        let rhs = xs.apply(&self.up_proj)?;
+        (lhs * rhs)?.apply(&self.down_proj)
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Attention {
+    q_proj: Linear,
+    k_proj: Linear,
+    v_proj: Linear,
+    o_proj: Linear,
+    num_heads: usize,
+    num_kv_heads: usize,
+    num_kv_groups: usize,
+    head_dim: usize,
+    hidden_size: usize,
+    rotary_emb: Arc<RotaryEmbedding>,
+    kv_cache: Option<(Tensor, Tensor)>,
+}
+
+impl Attention {
+    fn new(rotary_emb: Arc<RotaryEmbedding>, cfg: &Config, vb: VarBuilder) -> Result<Self> {
+        let hidden_sz = cfg.hidden_size;
+        let num_heads = cfg.num_attention_heads;
+        let num_kv_heads = cfg.num_key_value_heads;
+        let num_kv_groups = num_heads / num_kv_heads;
+        let head_dim = hidden_sz / num_heads;
+        let q_proj = linear(hidden_sz, num_heads * head_dim, vb.pp("q_proj"))?;
+        let k_proj = linear(hidden_sz, num_kv_heads * head_dim, vb.pp("k_proj"))?;
+        let v_proj = linear(hidden_sz, num_kv_heads * head_dim, vb.pp("v_proj"))?;
+        let o_proj = linear_no_bias(num_heads * head_dim, hidden_sz, vb.pp("o_proj"))?;
+        Ok(Self {
+            q_proj,
+            k_proj,
+            v_proj,
+            o_proj,
+            num_heads,
+            num_kv_heads,
+            num_kv_groups,
+            head_dim,
+            hidden_size: hidden_sz,
+            rotary_emb,
+            kv_cache: None,
+        })
+    }
+
+    fn repeat_kv(&self, xs: Tensor) -> Result<Tensor> {
+        let n_rep = self.num_kv_groups;
+        if n_rep == 1 {
+            Ok(xs)
+        } else {
+            let (b_sz, num_kv_heads, seq_len, head_dim) = xs.dims4()?;
+            xs.unsqueeze(2)?
+                .expand((b_sz, num_kv_heads, n_rep, seq_len, head_dim))?
+                .reshape((b_sz, num_kv_heads * n_rep, seq_len, head_dim))
+        }
+    }
+
+    fn forward(
+        &mut self,
+        xs: &Tensor,
+        attention_mask: Option<&Tensor>,
+        seqlen_offset: usize,
+    ) -> Result<Tensor> {
+        let (b_sz, q_len, _) = xs.dims3()?;
+
+        let query_states = self.q_proj.forward(xs)?;
+        let key_states = self.k_proj.forward(xs)?;
+        let value_states = self.v_proj.forward(xs)?;
+
+        let query_states = query_states
+            .reshape((b_sz, q_len, self.num_heads, self.head_dim))?
+            .transpose(1, 2)?;
+        let key_states = key_states
+            .reshape((b_sz, q_len, self.num_kv_heads, self.head_dim))?
+            .transpose(1, 2)?;
+        let value_states = value_states
+            .reshape((b_sz, q_len, self.num_kv_heads, self.head_dim))?
+            .transpose(1, 2)?;
+
+        let (query_states, key_states) =
+            self.rotary_emb
+                .apply_rotary_emb_qkv(&query_states, &key_states, seqlen_offset)?;
+
+        let (key_states, value_states) = match &self.kv_cache {
+            None => (key_states, value_states),
+            Some((prev_k, prev_v)) => {
+                let key_states = Tensor::cat(&[prev_k, &key_states], 2)?;
+                let value_states = Tensor::cat(&[prev_v, &value_states], 2)?;
+                (key_states, value_states)
+            }
+        };
+        self.kv_cache = Some((key_states.clone(), value_states.clone()));
+
+        let key_states = self.repeat_kv(key_states)?.contiguous()?;
+        let value_states = self.repeat_kv(value_states)?.contiguous()?;
+
+        let attn_output = {
+            let scale = 1f64 / f64::sqrt(self.head_dim as f64);
+            let attn_weights = (query_states.matmul(&key_states.transpose(2, 3)?)? * scale)?;
+
+            let attn_weights = match attention_mask {
+                None => attn_weights,
+                Some(mask) => attn_weights.broadcast_add(mask)?,
+            };
+            let attn_weights = candle_nn::ops::softmax_last_dim(&attn_weights)?;
+            attn_weights.matmul(&value_states)?
+        };
+        attn_output
+            .transpose(1, 2)?
+            .reshape((b_sz, q_len, self.hidden_size))?
+            .apply(&self.o_proj)
+    }
+
+    fn clear_kv_cache(&mut self) {
+        self.kv_cache = None
+    }
+}
+
+// https://github.com/huggingface/transformers/blob/536ea2aca234fb48c5c69769431d643b0d93b233/src/transformers/models/qwen2_moe/modeling_qwen2_moe.py#L800
+#[derive(Debug, Clone)]
+struct SparseMoeBlock {
+    gate: Linear,
+    experts: Vec<MLP>,
+    shared_expert: MLP,
+    shared_expert_gate: Linear,
+    norm_topk_prob: bool,
+    num_experts_per_tok: usize,
+}
+
+impl SparseMoeBlock {
+    fn new(cfg: &Config, vb: VarBuilder) -> Result<Self> {
+        let gate = linear_no_bias(cfg.hidden_size, cfg.num_experts, vb.pp("gate"))?;
+        let mut experts = Vec::with_capacity(cfg.num_experts);
+        let vb_e = vb.pp("experts");
+        for idx in 0..cfg.num_experts {
+            let expert = MLP::new(cfg.moe_intermediate_size, cfg, vb_e.pp(idx))?;
+            experts.push(expert)
+        }
+        let shared_expert = MLP::new(
+            cfg.shared_expert_intermediate_size,
+            cfg,
+            vb.pp("shared_expert"),
+        )?;
+        let shared_expert_gate = linear_no_bias(cfg.hidden_size, 1, vb.pp("shared_expert_gate"))?;
+        Ok(Self {
+            gate,
+            experts,
+            shared_expert,
+            shared_expert_gate,
+            norm_topk_prob: cfg.norm_topk_prob,
+            num_experts_per_tok: cfg.num_experts_per_tok,
+        })
+    }
+}
+
+impl Module for SparseMoeBlock {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        let (b_size, seq_len, hidden_dim) = xs.dims3()?;
+        let xs = xs.reshape(((), hidden_dim))?;
+        let router_logits = xs.apply(&self.gate)?;
+        let routing_weights = candle_nn::ops::softmax_last_dim(&router_logits)?;
+
+        // In order to extract topk, we extract the data from the tensor and manipulate it
+        // directly. Maybe we will want to use some custom ops instead at some point.
+        let routing_weights = routing_weights.to_dtype(DType::F32)?.to_vec2::<f32>()?;
+
+        // routing_weights, selected_experts = torch.topk(routing_weights, self.top_k, dim=-1)
+        // top_x contains the row indexes to evaluate for each expert.
+        let mut top_x = vec![vec![]; self.experts.len()];
+        let mut selected_experts = vec![vec![]; self.experts.len()];
+        for (row_idx, rw) in routing_weights.iter().enumerate() {
+            let mut dst = (0..rw.len() as u32).collect::<Vec<u32>>();
+            dst.sort_by(|&i, &j| rw[j as usize].total_cmp(&rw[i as usize]));
+            let mut sum_routing_weights = 0f32;
+            for &expert_idx in dst.iter().take(self.num_experts_per_tok) {
+                let expert_idx = expert_idx as usize;
+                let routing_weight = rw[expert_idx];
+                sum_routing_weights += routing_weight;
+                top_x[expert_idx].push(row_idx as u32);
+            }
+            for &expert_idx in dst.iter().take(self.num_experts_per_tok) {
+                let expert_idx = expert_idx as usize;
+                let routing_weight = if self.norm_topk_prob {
+                    rw[expert_idx] / sum_routing_weights
+                } else {
+                    rw[expert_idx]
+                };
+                selected_experts[expert_idx].push(routing_weight)
+            }
+        }
+
+        let mut ys = xs.zeros_like()?;
+        for (expert_idx, expert_layer) in self.experts.iter().enumerate() {
+            let top_x = &top_x[expert_idx];
+            if top_x.is_empty() {
+                continue;
+            }
+            let top_x = Tensor::new(top_x.as_slice(), xs.device())?;
+            let selected_experts =
+                Tensor::new(selected_experts[expert_idx].as_slice(), xs.device())?
+                    .reshape(((), 1))?
+                    .to_dtype(xs.dtype())?;
+            // Index the correct hidden states and compute the expert hidden state for
+            // the current expert. We need to make sure to multiply the output hidden
+            // states by `routing_weights` on the corresponding tokens (top-1 and top-2)
+            let current_state = xs.index_select(&top_x, 0)?.reshape(((), hidden_dim))?;
+            // current_hidden_states = expert_layer(current_state, routing_weights[top_x_list, idx_list, None])
+            let current_hidden_states = expert_layer.forward(&current_state)?;
+            let current_hidden_states = current_hidden_states.broadcast_mul(&selected_experts)?;
+            ys = ys.index_add(&top_x, &current_hidden_states, 0)?;
+        }
+        let shared_expert_output = xs.apply(&self.shared_expert)?;
+        let shared_expert_output = shared_expert_output.broadcast_mul(&candle_nn::ops::sigmoid(
+            &xs.apply(&self.shared_expert_gate)?,
+        )?)?;
+        let ys = (ys + shared_expert_output)?;
+        let ys = ys.reshape((b_size, seq_len, hidden_dim))?;
+        Ok(ys)
+    }
+}
+
+#[derive(Debug, Clone)]
+enum MlpOrMoeBlock {
+    Mlp(MLP),
+    MoeBlock(SparseMoeBlock),
+}
+
+impl Module for MlpOrMoeBlock {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        match self {
+            Self::MoeBlock(m) => m.forward(xs),
+            Self::Mlp(m) => m.forward(xs),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct DecoderLayer {
+    self_attn: Attention,
+    mlp: MlpOrMoeBlock,
+    input_layernorm: RmsNorm,
+    post_attention_layernorm: RmsNorm,
+}
+
+impl DecoderLayer {
+    fn new(
+        layer_idx: usize,
+        rotary_emb: Arc<RotaryEmbedding>,
+        cfg: &Config,
+        vb: VarBuilder,
+    ) -> Result<Self> {
+        let self_attn = Attention::new(rotary_emb, cfg, vb.pp("self_attn"))?;
+        let mlp = if cfg.num_experts > 0 && (layer_idx + 1) % cfg.decoder_sparse_step == 0 {
+            MlpOrMoeBlock::MoeBlock(SparseMoeBlock::new(cfg, vb.pp("mlp"))?)
+        } else {
+            MlpOrMoeBlock::Mlp(MLP::new(cfg.intermediate_size, cfg, vb.pp("mlp"))?)
+        };
+        let input_layernorm =
+            RmsNorm::new(cfg.hidden_size, cfg.rms_norm_eps, vb.pp("input_layernorm"))?;
+        let post_attention_layernorm = RmsNorm::new(
+            cfg.hidden_size,
+            cfg.rms_norm_eps,
+            vb.pp("post_attention_layernorm"),
+        )?;
+        Ok(Self {
+            self_attn,
+            mlp,
+            input_layernorm,
+            post_attention_layernorm,
+        })
+    }
+
+    fn forward(
+        &mut self,
+        xs: &Tensor,
+        attention_mask: Option<&Tensor>,
+        seqlen_offset: usize,
+    ) -> Result<Tensor> {
+        let residual = xs;
+        let xs = self.input_layernorm.forward(xs)?;
+        let xs = self.self_attn.forward(&xs, attention_mask, seqlen_offset)?;
+        let xs = (xs + residual)?;
+        let residual = &xs;
+        let xs = xs.apply(&self.post_attention_layernorm)?.apply(&self.mlp)?;
+        residual + xs
+    }
+
+    fn clear_kv_cache(&mut self) {
+        self.self_attn.clear_kv_cache()
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Model {
+    embed_tokens: candle_nn::Embedding,
+    layers: Vec<DecoderLayer>,
+    norm: RmsNorm,
+    lm_head: Linear,
+    sliding_window: usize,
+    device: Device,
+    dtype: DType,
+}
+
+impl Model {
+    pub fn new(cfg: &Config, vb: VarBuilder) -> Result<Self> {
+        let vb_m = vb.pp("model");
+        let embed_tokens =
+            candle_nn::embedding(cfg.vocab_size, cfg.hidden_size, vb_m.pp("embed_tokens"))?;
+        let rotary_emb = Arc::new(RotaryEmbedding::new(vb.dtype(), cfg, vb_m.device())?);
+        let mut layers = Vec::with_capacity(cfg.num_hidden_layers);
+        let vb_l = vb_m.pp("layers");
+        for layer_idx in 0..cfg.num_hidden_layers {
+            let layer = DecoderLayer::new(layer_idx, rotary_emb.clone(), cfg, vb_l.pp(layer_idx))?;
+            layers.push(layer)
+        }
+        let norm = RmsNorm::new(cfg.hidden_size, cfg.rms_norm_eps, vb_m.pp("norm"))?;
+        let lm_head = linear_no_bias(cfg.hidden_size, cfg.vocab_size, vb.pp("lm_head"))?;
+        Ok(Self {
+            embed_tokens,
+            layers,
+            norm,
+            lm_head,
+            sliding_window: cfg.sliding_window,
+            device: vb.device().clone(),
+            dtype: vb.dtype(),
+        })
+    }
+
+    fn prepare_decoder_attention_mask(
+        &self,
+        b_size: usize,
+        tgt_len: usize,
+        seqlen_offset: usize,
+    ) -> Result<Tensor> {
+        // Sliding window mask?
+        let mask: Vec<_> = (0..tgt_len)
+            .flat_map(|i| {
+                (0..tgt_len).map(move |j| {
+                    if i < j || j + self.sliding_window < i {
+                        f32::NEG_INFINITY
+                    } else {
+                        0.
+                    }
+                })
+            })
+            .collect();
+        let mask = Tensor::from_slice(&mask, (tgt_len, tgt_len), &self.device)?;
+        let mask = if seqlen_offset > 0 {
+            let mask0 = Tensor::zeros((tgt_len, seqlen_offset), DType::F32, &self.device)?;
+            Tensor::cat(&[&mask0, &mask], D::Minus1)?
+        } else {
+            mask
+        };
+        mask.expand((b_size, 1, tgt_len, tgt_len + seqlen_offset))?
+            .to_dtype(self.dtype)
+    }
+
+    pub fn forward(&mut self, input_ids: &Tensor, seqlen_offset: usize) -> Result<Tensor> {
+        let (b_size, seq_len) = input_ids.dims2()?;
+        let attention_mask = if seq_len <= 1 {
+            None
+        } else {
+            let mask = self.prepare_decoder_attention_mask(b_size, seq_len, seqlen_offset)?;
+            Some(mask)
+        };
+        let mut xs = self.embed_tokens.forward(input_ids)?;
+        for layer in self.layers.iter_mut() {
+            xs = layer.forward(&xs, attention_mask.as_ref(), seqlen_offset)?
+        }
+        xs.narrow(1, seq_len - 1, 1)?
+            .apply(&self.norm)?
+            .apply(&self.lm_head)
+    }
+
+    pub fn clear_kv_cache(&mut self) {
+        for layer in self.layers.iter_mut() {
+            layer.clear_kv_cache()
+        }
+    }
+}