nn: share attention code across sam, swin and dino

Author: Acly

src/visp/arch/dino.cpp

@@ -55,42 +55,27 @@ tensor mlp(model_ref m, tensor x) {
     return x;
 }
 
-tensor attention(model_ref m, tensor x, int n_heads) {
+tensor self_attention(model_ref m, tensor x, int n_heads) {
     auto [c, n, b, _] = nelements(x);
-    float scale = 1.0f / std::sqrt(float(c) / float(n_heads));
-    bool flash_attn = bool(m.flags & model_build_flag::flash_attention);
-    ggml_type kv_type = flash_attn ? GGML_TYPE_F16 : GGML_TYPE_F32;
-
-    auto split = [=](model_ref m, tensor x, ggml_type type, bool transpose = false) mutable {
-        x = linear(m, x);
-        x = ggml_reshape_4d(m, x, c / n_heads, n_heads, n, b);
-        x = transpose ? ggml_permute(m, x, 1, 2, 0, 3) : ggml_permute(m, x, 0, 2, 1, 3);
-        return ggml_cast(m, x, type);
+    auto project = [&](model_ref m, tensor t) {
+        t = linear(m, t);
+        t = ggml_reshape_4d(m, t, c / n_heads, n_heads, n, b);
+        return t;
     };
 
-    tensor q = split(m["attention.query"], x, GGML_TYPE_F32);
-    tensor k = split(m["attention.key"], x, kv_type);
-    tensor v = split(m["attention.value"], x, kv_type, !flash_attn);
-
-    if (flash_attn) {
-        x = ggml_flash_attn_ext(m, q, k, v, nullptr, scale, 0.0f, 0.0f);
-    } else {
-        tensor attn = ggml_mul_mat(m, k, q);
-        attn = ggml_soft_max_ext(m, attn, nullptr, scale, 0.0f);
-
-        x = ggml_mul_mat(m, v, attn);
-        x = ggml_cont(m, ggml_permute(m, x, 0, 2, 1, 3));
-    }
+    tensor q = project(m["attention.query"], x);
+    tensor k = project(m["attention.key"], x);
+    tensor v = project(m["attention.value"], x);
 
-    x = ggml_reshape_3d(m, x, c, n, b);
-    x = linear(m["output.dense"], x);
-    return named(m, x);
+    float scale = 1.0f / std::sqrt(float(c) / float(n_heads));
+    x = attention(m, q, k, v, nullptr, scale, m["output.dense"]);
+    return x;
 }
 
 tensor layer(model_ref m, tensor x, dino_params const& p) {
     tensor attn = x;
     attn = layer_norm(m["norm1"], attn, 1e-6f);
-    attn = attention(m["attention"], attn, p.n_heads);
+    attn = self_attention(m["attention"], attn, p.n_heads);
     attn = layer_scale(m["layer_scale1"], attn);
     x = ggml_add(m, x, attn);
 

src/visp/arch/dino.h

@@ -12,7 +12,7 @@ tensor interpolate_pos_encoding(model_ref m, tensor x, int64_t w, int64_t h, int
 tensor prepare_tokens(model_ref m, tensor x, int patch_size);
 tensor layer_scale(model_ref m, tensor x);
 tensor mlp(model_ref m, tensor x);
-tensor attention(model_ref m, tensor x, int n_heads);
+tensor self_attention(model_ref m, tensor x, int n_heads);
 tensor layer(model_ref m, tensor x, dino_params const& p);
 
 std::vector<tensor> get_intermediate_layers(

src/visp/arch/mobile-sam.cpp

@@ -121,54 +121,14 @@ tensor mlp(model_ref m, tensor x) {
     return named(m, x);
 }
 
-tensor attention_rel_bias(model_ref m, tensor x, int dim, int num_heads) {
-    GGML_ASSERT(dim % num_heads == 0);
-    int key_dim = dim / num_heads;
-    auto [c, n, b, _] = nelements(x);
-
-    x = layer_norm(m["norm"], x);
-
-    tensor qkv = linear(m["qkv"], x);
-    qkv = ggml_reshape_4d(m, qkv, key_dim, 3, num_heads * n, b);
-    qkv = ggml_cont(m, ggml_permute(m, qkv, 0, 3, 1, 2)); // ne = [key_dim, num_heads * n, b, 3]
-
-    auto split = [=](model_ref m, tensor tensor, int64_t index) {
-        tensor = slice(m, tensor, {}, {}, {}, index);
-        tensor = ggml_reshape_4d(m, tensor, key_dim, num_heads, n, b);
-        return tensor;
-    };
-
-    tensor q = split(m, qkv, 0);
-    tensor k = split(m, qkv, 1);
-    tensor v = split(m, qkv, 2);
+tensor attention_rel_bias(model_ref m, tensor x, int dim, int n_heads) {
+    float scale = 1.0f / std::sqrt(float(dim / n_heads));
     tensor mask = m.weights("attention_biases_indexed");
-    float scale = 1.0f / std::sqrt(float(key_dim));
-
-    if (m.flags & model_build_flag::flash_attention) {
-        q = ggml_cont(m, ggml_permute(m, q, 0, 2, 1, 3));
-        k = ggml_cast(m, ggml_permute(m, k, 0, 2, 1, 3), GGML_TYPE_F16);
-        v = ggml_cast(m, ggml_permute(m, v, 0, 2, 1, 3), GGML_TYPE_F16);
-        if (mask->type != GGML_TYPE_F16) {
-            mask = ggml_cast(m, mask, GGML_TYPE_F16);
-        }
-
-        x = ggml_flash_attn_ext(m, q, k, v, mask, scale, 0.0f, 0.0f);
-        ggml_flash_attn_ext_set_prec(x, GGML_PREC_F32);
-    } else {
-        q = ggml_cont(m, ggml_permute(m, q, 0, 2, 1, 3));
-        k = ggml_cont(m, ggml_permute(m, k, 0, 2, 1, 3));
-        v = ggml_cont(m, ggml_permute(m, v, 1, 2, 0, 3)); // transpose for mul_mat later
 
-        tensor attn = ggml_mul_mat(m, k, q); // q @ k (k is transposed in mul_mat)
-        attn = ggml_soft_max_ext(m, attn, mask, scale, 0.0f);
-
-        x = ggml_mul_mat(m, v, attn);                     // attn @ v
-        x = ggml_cont(m, ggml_permute(m, x, 0, 2, 1, 3)); // transpose(1, 2)
-    }
-    x = ggml_reshape_3d(m, x, key_dim * num_heads, n, b);
-    x = linear(m["proj"], x);
-
-    return named(m, x);
+    x = layer_norm(m["norm"], x);
+    auto [q, k, v] = split_qkv(m["qkv"], x, n_heads, 1);
+    x = attention(m, q, k, v, mask, scale, m["proj"]);
+    return x;
 }
 
 tensor tiny_vit_block(
@@ -344,25 +304,18 @@ tensor separate_attention_heads(model_ref m, tensor x, int num_heads) {
     return x;
 }
 
-tensor attention(model_ref m, tensor q, tensor k, tensor v, int num_heads) {
+tensor decoder_attention(model_ref m, tensor q, tensor k, tensor v, int n_heads) {
     q = linear(m["q_proj"], q);
     k = linear(m["k_proj"], k);
     v = linear(m["v_proj"], v);
 
-    q = separate_attention_heads(m, q, num_heads);
-    k = separate_attention_heads(m, k, num_heads);
-    v = ggml_reshape_4d(m, v, v->ne[0] / num_heads, num_heads, v->ne[1], v->ne[2]);
-    v = ggml_cont(m, ggml_permute(m, v, 1, 2, 0, 3)); // already transposed for mul_mat
+    q = ggml_reshape_4d(m, q, q->ne[0] / n_heads, n_heads, q->ne[1], q->ne[2]);
+    k = ggml_reshape_4d(m, k, k->ne[0] / n_heads, n_heads, k->ne[1], k->ne[2]);
+    v = ggml_reshape_4d(m, v, v->ne[0] / n_heads, n_heads, v->ne[1], v->ne[2]);
 
-    tensor attn = ggml_mul_mat(m, k, q);
-    attn = ggml_scale_inplace(m, attn, 1.0f / std::sqrt(float(q->ne[0])));
-    attn = ggml_soft_max(m, attn);
-
-    tensor out = ggml_mul_mat(m, v, attn);
-    out = ggml_cont(m, ggml_permute(m, out, 0, 2, 1, 3));
-    out = ggml_reshape_3d(m, out, out->ne[0] * out->ne[1], out->ne[2], out->ne[3]);
-    out = linear(m["out_proj"], out);
-    return out;
+    float scale = 1.0f / std::sqrt(float(q->ne[0]));
+    tensor x = attention(m, q, k, v, nullptr, scale, m["out_proj"]);
+    return x;
 }
 
 auto two_way_attention_block(
@@ -375,18 +328,18 @@ auto two_way_attention_block(
     bool skip_first_layer_pe) -> std::tuple<tensor, tensor> {
     // Self attention block
     if (skip_first_layer_pe) {
-        queries = attention(m["self_attn"], queries, queries, queries, num_heads);
+        queries = decoder_attention(m["self_attn"], queries, queries, queries, num_heads);
     } else {
         tensor q = ggml_add(m, queries, query_pe);
-        tensor attn_out = attention(m["self_attn"], q, q, queries, num_heads);
+        tensor attn_out = decoder_attention(m["self_attn"], q, q, queries, num_heads);
         queries = ggml_add(m, queries, attn_out);
     }
     queries = layer_norm(m["norm1"], queries);
 
     // Cross attention block, tokens attending to image embedding
     tensor q = ggml_add(m, queries, query_pe);
     tensor k = ggml_add(m, keys, key_pe);
-    tensor attn_out = attention(m["cross_attn_t2i"], q, k, keys, num_heads);
+    tensor attn_out = decoder_attention(m["cross_attn_t2i"], q, k, keys, num_heads);
     queries = ggml_add_inplace(m, queries, attn_out);
     queries = layer_norm(m["norm2"], queries);
 
@@ -401,7 +354,7 @@ auto two_way_attention_block(
     // Cross attention block, image embedding attending to tokens
     q = ggml_add(m, queries, query_pe);
     // k = ggml_add(m, keys, key_pe); // redundant, same as above
-    attn_out = attention(m["cross_attn_i2t"], k, q, queries, num_heads);
+    attn_out = decoder_attention(m["cross_attn_i2t"], k, q, queries, num_heads);
     keys = ggml_add_inplace(m, keys, attn_out);
     keys = layer_norm(m["norm4"], keys);
 
@@ -434,7 +387,7 @@ auto two_way_transformer(
     // Apply the final attention layer from the points to the image
     tensor q = ggml_add(m, queries, point_embedding);
     tensor k = ggml_add(m, keys, image_pe);
-    tensor attn_out = attention(m["final_attn_t2i"], q, k, keys, num_heads);
+    tensor attn_out = decoder_attention(m["final_attn_t2i"], q, k, keys, num_heads);
     queries = ggml_add_inplace(m, queries, attn_out);
     queries = layer_norm(m["norm_final_attn"], queries);
 

src/visp/arch/mobile-sam.h

@@ -66,7 +66,7 @@ tensor position_embedding_random(model_ref m, tensor coords);
 
 tensor mlp_block(model_ref m, tensor x);
 tensor separate_attention_heads(model_ref m, tensor x, int num_heads);
-tensor attention(model_ref m, tensor q, tensor k, tensor v, int num_heads);
+tensor decoder_attention(model_ref m, tensor q, tensor k, tensor v, int num_heads);
 std::tuple<tensor, tensor> two_way_attention_block(
     model_ref m,
     tensor queries,

src/visp/arch/swin.cpp

@@ -65,24 +65,6 @@ tensor window_reverse(model_ref m, tensor x, int64_t w, int64_t h, int window) {
 
 tensor window_attention(model_ref m, tensor x, tensor mask, int n_heads, int window) {
     auto [c, n, b, _] = nelements(x);
-    float scale = 1.0f / std::sqrt(float(c / n_heads));
-    bool flash_attn = bool(m.flags & model_build_flag::flash_attention);
-    ggml_type kv_type = flash_attn ? GGML_TYPE_F16 : GGML_TYPE_F32;
-
-    tensor qkv = linear(m["qkv"], x);
-    qkv = ggml_reshape_4d(m, qkv, c / n_heads, n_heads, 3, n * b);
-    qkv = ggml_cont(m, ggml_permute(m, qkv, 0, 1, 3, 2));
-
-    auto split = [=](tensor t, size_t index, ggml_type type, bool transpose = false) mutable {
-        t = slice(m, t, {}, {}, {}, index);
-        t = ggml_reshape_4d(m, t, c / n_heads, n_heads, n, b);
-        t = transpose ? ggml_permute(m, t, 1, 2, 0, 3) : ggml_permute(m, t, 0, 2, 1, 3);
-        t = ggml_cast(m, t, type); // TODO: future flash attention supports f32 and permutations
-        return t;
-    };
-    tensor q = split(qkv, 0, GGML_TYPE_F32);
-    tensor k = split(qkv, 1, kv_type);
-    tensor v = split(qkv, 2, kv_type, !flash_attn);
 
     tensor_name rel_pos_name = format<tensor_name>("window_attention_{}.rel_pos_index", window);
     tensor rel_pos_index = ggml_get_tensor(m, rel_pos_name.c_str());
@@ -104,19 +86,10 @@ tensor window_attention(model_ref m, tensor x, tensor mask, int n_heads, int win
         attn_mask = ggml_add(m, mask, attn_mask);         // [n, n, n_heads, b] + [n, n, n_heads, 1]
     }
 
-    if (flash_attn) {
-        x = ggml_flash_attn_ext(m, q, k, v, attn_mask, scale, 0.0f, 0.0f);
-        ggml_flash_attn_ext_set_prec(x, GGML_PREC_F32);
-    } else {
-        tensor attn = ggml_mul_mat(m, k, q);
-        attn = ggml_soft_max_ext(m, attn, attn_mask, scale, 0.0f);
-
-        x = ggml_mul_mat(m, v, attn);
-        x = ggml_cont(m, ggml_permute(m, x, 0, 2, 1, 3));
-    }
+    auto [q, k, v] = split_qkv(m["qkv"], x, n_heads, 2);
+    float scale = 1.0f / std::sqrt(float(c / n_heads));
+    x = attention(m, q, k, v, attn_mask, scale, m["proj"]);
 
-    x = ggml_reshape_3d(m, x, c, n, b);
-    x = linear(m["proj"], x);
     return named(m, x);
 }
 

src/visp/nn.cpp

@@ -80,7 +80,7 @@ tensor conv_2d(model_ref m, tensor x, int stride, int pad) {
             x = ggml_mul_mat(m, weight, x);
             x = ggml_reshape_4d(m, x, weight->ne[1], w, h, b);
 
-        } else if (m.flags & model_build_flag::conv_2d_direct_cwhn) { 
+        } else if (m.flags & model_build_flag::conv_2d_direct_cwhn) {
             weight = permute_cwhn_to_whcn(m, weight);
             x = permute_cwhn_to_whcn(m, x);
             x = ggml_conv_2d_direct(m, weight, x, stride, stride, pad, pad, 1, 1);
@@ -144,7 +144,7 @@ tensor conv_2d_deform(
         }
     }
     x = ggml_conv_2d_deform(m, weight, x, offset, mask, stride, stride, pad, pad);
-    
+
     if (m.flags & model_build_flag::cwhn) {
         x = permute_whcn_to_cwhn(m, x);
     }
@@ -183,4 +183,68 @@ tensor patch_embed(model_ref m, tensor x, int patch_size) {
     return named(m, x);
 }
 
+attention_qkv split_qkv(model_ref m, tensor x, int n_heads, int split_dim) {
+    auto [c, n, b, _] = nelements(x);
+
+    tensor qkv = linear(m, x);
+    switch (split_dim) {
+        case 1:
+            qkv = ggml_reshape_4d(m, qkv, c / n_heads, 3, n_heads * n, b);
+            qkv = ggml_cont(m, ggml_permute(m, qkv, 0, 3, 1, 2));
+            break;
+        case 2:
+            qkv = ggml_reshape_4d(m, qkv, c / n_heads, n_heads, 3, n * b);
+            qkv = ggml_cont(m, ggml_permute(m, qkv, 0, 1, 3, 2));
+            break;
+        default: ASSERT(false, "Unsupported split_dim");
+    }
+
+    auto split = [&](tensor t, size_t index) mutable {
+        t = slice(m, t, {}, {}, {}, index);
+        t = ggml_reshape_4d(m, t, c / n_heads, n_heads, n, b);
+        return t;
+    };
+
+    tensor q = split(qkv, 0);
+    tensor k = split(qkv, 1);
+    tensor v = split(qkv, 2);
+    return {q, k, v};
+}
+
+tensor attention(
+    model_ref m, tensor q, tensor k, tensor v, tensor mask, float scale, model_ref m_out) {
+
+    q = ggml_permute(m, q, 0, 2, 1, 3);
+    k = ggml_permute(m, k, 0, 2, 1, 3);
+
+    tensor x = nullptr;
+    if (m.flags & model_build_flag::flash_attention) {
+        v = ggml_permute(m, v, 0, 2, 1, 3);
+
+        k = ggml_cast(m, k, GGML_TYPE_F16);
+        v = ggml_cast(m, v, GGML_TYPE_F16);
+        if (mask && mask->type != GGML_TYPE_F16) {
+            mask = ggml_cast(m, mask, GGML_TYPE_F16);
+        }
+
+        x = ggml_flash_attn_ext(m, q, k, v, mask, scale, 0.0f, 0.0f);
+        ggml_flash_attn_ext_set_prec(x, GGML_PREC_F32);
+
+    } else {
+        v = ggml_cont(m, ggml_permute(m, v, 1, 2, 0, 3));
+
+        tensor attn = ggml_mul_mat(m, k, q);
+        attn = ggml_soft_max_ext(m, attn, mask, scale, 0.0f);
+        x = ggml_mul_mat(m, v, attn);
+
+        x = ggml_cont(m, ggml_permute(m, x, 0, 2, 1, 3));
+    }
+
+    // [head_dim, n_heads, n_patches, batch] -> [embed_dim, n_patches, batch]
+    x = ggml_reshape_3d(m, x, x->ne[0] * x->ne[1], x->ne[2], x->ne[3]);
+    x = linear(m_out, x);
+
+    return named(m, x);
+}
+
 } // namespace visp

src/visp/nn.h

@@ -41,4 +41,15 @@ tensor batch_norm_2d(model_ref, tensor x);
 // 2D image to patch embedding using convolution and optional norm. CWHN input and output.
 tensor patch_embed(model_ref, tensor x, int patch_size);
 
+struct attention_qkv {
+    tensor q, k, v;
+};
+// Input: x [head_dim*n_heads, n_patches, batch]
+// Output: q, k, v each of shape [head_dim, n_heads, n_patches, batch]
+attention_qkv split_qkv(model_ref m, tensor x, int n_heads, int split_dim);
+
+// Attention with optional mask and output linear layer.
+tensor attention(
+    model_ref m, tensor q, tensor k, tensor v, tensor mask, float scale, model_ref m_out);
+
 } // namespace visp

tests/workbench.cpp

@@ -205,7 +205,7 @@ DEF(sam_attention)(model_ref m, span<tensor> input, param_dict const& p) {
     tensor q = input[0];
     tensor k = m.weights("input_k");
     tensor v = m.weights("input_v");
-    return {sam::attention(m, q, k, v, 2)};
+    return {sam::decoder_attention(m, q, k, v, 2)};
 }
 
 DEF(sam_two_way_attention_block)(model_ref m, span<tensor> input, param_dict const& p) {
@@ -443,7 +443,7 @@ DEF(dino_attention)(model_ref m, span<tensor> input, param_dict const& p) {
     if (p.get("flash_attn", 0) != 0) {
         m.flags |= model_build_flag::flash_attention;
     }
-    return {dino::attention(m, input[0], p.get("n_heads", 8))};
+    return {dino::self_attention(m, input[0], p.get("n_heads", 8))};
 }
 
 DEF(dino_block)(model_ref m, span<tensor> input, param_dict const& p) {