Fix PaliGemma models.

PiperOrigin-RevId: 736483021

Author: pculliton

gemma/configs.cc

@@ -291,6 +291,7 @@ ModelConfig GetVitConfig(const ModelConfig& config) {
   vit_config.seq_len = config.vit_config.seq_len;
   vit_config.layer_configs = config.vit_config.layer_configs;
   vit_config.pool_dim = config.vit_config.pool_dim;
+  vit_config.wrapping = config.wrapping;
   // The Vit part does not have a vocabulary, the image patches are embedded.
   vit_config.vocab_size = 0;
   return vit_config;

gemma/gemma-inl.h

@@ -20,6 +20,7 @@
 #include <stdio.h>
 
 #include <algorithm>  // std::min
+#include <cstdio>
 #include <vector>
 
 #include "compression/compress.h"
@@ -610,7 +611,7 @@ class VitAttention {
   }
 
   // TODO(philculliton): transition fully to MatMul.
-  HWY_NOINLINE void DotSoftmaxWeightedSum() {
+  HWY_NOINLINE void DotSoftmaxWeightedSumMatrix() {
     const size_t qkv_dim = layer_config_.qkv_dim;
     const size_t heads = layer_config_.heads;
     HWY_ASSERT_M(heads == layer_config_.kv_heads, "Vit expects MHA");
@@ -669,6 +670,44 @@ class VitAttention {
     }
   }
 
+  HWY_NOINLINE void DotSoftmaxWeightedSum() {
+    const size_t qkv_dim = layer_config_.qkv_dim;
+    const size_t heads = layer_config_.heads;
+    HWY_ASSERT_M(heads == layer_config_.kv_heads, "Vit expects MHA");
+    const size_t seq_len = activations_.seq_len;
+    const float query_scale = 1.0f / sqrtf(static_cast<float>(qkv_dim));
+    PROFILER_ZONE("Gen.VitAttention.DotSoftmax");
+
+    // Compute Q.K, softmax, and weighted V.
+    pool_.Run(0, layer_config_.heads * num_tokens_,
+              [&](uint64_t task, size_t /*thread*/) HWY_ATTR {
+                const size_t head = task % layer_config_.heads;
+                const size_t token = task / layer_config_.heads;
+                // Compute Q.K scores, which are "logits" stored in head_att.
+                float* HWY_RESTRICT q =
+                    activations_.q.Batch(token) + head * 3 * qkv_dim;
+                MulByConst(query_scale, q, qkv_dim);
+                float* HWY_RESTRICT head_att =
+                    activations_.att.Batch(token) + head * activations_.seq_len;
+                for (size_t i = 0; i < seq_len; ++i) {
+                  float* HWY_RESTRICT k =
+                      activations_.q.Batch(i) + head * 3 * qkv_dim + qkv_dim;
+                  head_att[i] = Dot(q, k, qkv_dim);  // score = q.k
+                }
+                // SoftMax yields "probabilities" in head_att.
+                Softmax(head_att, seq_len);
+                // Compute weighted sum of v into att_out.
+                float* HWY_RESTRICT att_out =
+                    activations_.att_out.Batch(token) + head * qkv_dim;
+                hwy::ZeroBytes(att_out, qkv_dim * sizeof(*att_out));
+                for (size_t i = 0; i < seq_len; ++i) {
+                  float* HWY_RESTRICT v = activations_.q.Batch(i) +
+                                          head * 3 * qkv_dim + 2 * qkv_dim;
+                  MulByConstAndAdd(head_att[i], v, att_out, qkv_dim);
+                }
+              });
+  }
+
   // Sums encoded (`att_out`) over num_heads (`layer_config_.heads`) and
   // head_dim (`qkv_dim`) into output (`att_sums`).
   HWY_NOINLINE void SumHeads() {
@@ -695,7 +734,11 @@ class VitAttention {
 
   HWY_INLINE void operator()() {
     ComputeQKV();
-    DotSoftmaxWeightedSum();
+    if (activations_.weights_config.wrapping == PromptWrapping::GEMMA_VLM) {
+      DotSoftmaxWeightedSumMatrix();
+    } else {
+      DotSoftmaxWeightedSum();
+    }
     SumHeads();
   }
 
@@ -1177,11 +1220,13 @@ HWY_NOINLINE void PrefillVit(const ModelWeightsPtrs<T>& weights,
                    weights.vit_encoder_norm_bias.data_scale1(),
                    activations.x.All(), vit_model_dim);
 
-  activations.x = AvgPool4x4(activations.x);
+  if (weights.weights_config.wrapping == PromptWrapping::GEMMA_VLM) {
+    activations.x = AvgPool4x4(activations.x);
 
-  // Apply soft embedding norm before input projection.
-  RMSNormInplace(weights.mm_embed_norm.data_scale1(), activations.x.All(),
-                 vit_model_dim);
+    // Apply soft embedding norm before input projection.
+    RMSNormInplace(weights.mm_embed_norm.data_scale1(), activations.x.All(),
+                   vit_model_dim);
+  }
 
   // Apply head embedding into image_tokens of size of the LLM kModelDim.
   MatMul(ConstMatFromBatch(activations.x.BatchSize(), activations.x),

gemma/run.cc

@@ -217,8 +217,11 @@ void ReplGemma(Gemma& model, KVCache& kv_cache, const AppArgs& app,
                    timing_info);
     std::cout << "\n\n";
 
-    // Prepare for the next turn.
+    // Prepare for the next turn. Works only for PaliGemma.
     if (!args.multiturn || model.Info().wrapping == PromptWrapping::PALIGEMMA) {
+      abs_pos = 0;  // Start a new turn at position 0.
+      InitGenerator(args, gen);
+    } else {
       // The last token was either EOS, then it should be ignored because it is
       // never part of the dialog, see Table 5 in the Gemma-2 paper:
       // https://arxiv.org/pdf/2408.00118

gemma/weights.h

@@ -500,7 +500,9 @@ struct ModelWeightsPtrs {
       GEMMA_CALL_FUNC(vit_img_pos_embedding);
       GEMMA_CALL_FUNC(vit_img_head_bias);
       GEMMA_CALL_FUNC(vit_img_head_kernel);
-      GEMMA_CALL_FUNC(mm_embed_norm);
+
+      if (ptrs[0]->weights_config.wrapping == PromptWrapping::GEMMA_VLM)
+        GEMMA_CALL_FUNC(mm_embed_norm);
     }
 
     for (int layer_idx = 0; layer_idx < ptrs[0]->c_layers.size(); ++layer_idx) {