vulkan: Implement "fast divide" (mul+shift) for unary ops like copy

Author: jeffbolznv

ggml/src/ggml-vulkan/ggml-vulkan.cpp

@@ -352,7 +352,45 @@ struct vk_op_unary_push_constants {
     uint32_t ne10; uint32_t ne11; uint32_t ne12; uint32_t ne13; uint32_t nb10; uint32_t nb11; uint32_t nb12; uint32_t nb13;
     uint32_t d_offset;
     float param1; float param2;
+    uint32_t ne0_012mp; uint32_t ne0_012L;
+    uint32_t ne0_01mp;  uint32_t ne0_01L;
+    uint32_t ne0_0mp;   uint32_t ne0_0L;
+    uint32_t ne1_012mp; uint32_t ne1_012L;
+    uint32_t ne1_01mp;  uint32_t ne1_01L;
+    uint32_t ne1_0mp;   uint32_t ne1_0L;
 };
+static_assert(sizeof(vk_op_unary_push_constants) <= 128, "sizeof(vk_op_unary_push_constants) must be <= 128");
+
+// See https://gmplib.org/~tege/divcnst-pldi94.pdf figure 4.1.
+// Precompute mp (m' in the paper) and L such that division
+// can be computed using a multiply (high 32b of 64b result)
+// and a shift:
+//
+// n/d = (mulhi(n, mp) + n) >> L;
+void init_fastdiv_values(uint32_t d, uint32_t &mp, uint32_t &L)
+{
+    // compute L = ceil(log2(d));
+    L = 0;
+    while (L < 32 && (uint32_t{1} << L) < d) {
+        L++;
+    }
+
+    mp = (uint32_t)((uint64_t{1} << 32) * ((uint64_t{1} << L) - d) / d + 1);
+}
+
+template <typename T> void init_pushconst_fastdiv(T &p) {
+    static_assert(!std::is_const<T>::value, "unexpected type");
+}
+
+template <> void init_pushconst_fastdiv(vk_op_unary_push_constants &p) {
+    // Compute magic values to divide by these six numbers.
+    init_fastdiv_values(p.ne02*p.ne01*p.ne00,  p.ne0_012mp,    p.ne0_012L);
+    init_fastdiv_values(p.ne01*p.ne00,         p.ne0_01mp,     p.ne0_01L);
+    init_fastdiv_values(p.ne00,                p.ne0_0mp,      p.ne0_0L);
+    init_fastdiv_values(p.ne12*p.ne11*p.ne10,  p.ne1_012mp,    p.ne1_012L);
+    init_fastdiv_values(p.ne11*p.ne10,         p.ne1_01mp,     p.ne1_01L);
+    init_fastdiv_values(p.ne10,                p.ne1_0mp,      p.ne1_0L);
+}
 
 struct vk_op_binary_push_constants {
     uint32_t ne;
@@ -2885,13 +2923,14 @@ static void ggml_vk_cpy_to_contiguous(ggml_backend_vk_context * ctx, vk_context&
         elements = { ne, 1, 1 };
     }
 
-    const vk_op_unary_push_constants pc = {
+    vk_op_unary_push_constants pc = {
         (uint32_t)ne,
         (uint32_t)tensor->ne[0], (uint32_t)tensor->ne[1], (uint32_t)tensor->ne[2], (uint32_t)tensor->ne[3], (uint32_t)tensor->nb[0] / tensor_type_size, (uint32_t)tensor->nb[1] / tensor_type_size, (uint32_t)tensor->nb[2] / tensor_type_size, (uint32_t)tensor->nb[3] / tensor_type_size,
         (uint32_t)tensor->ne[0], (uint32_t)tensor->ne[1], (uint32_t)tensor->ne[2], (uint32_t)tensor->ne[3],                       1                   , (uint32_t)tensor->ne[0]                   , (uint32_t)(tensor->ne[0] * tensor->ne[1]) , (uint32_t)(tensor->ne[0] * tensor->ne[1] * tensor->ne[2]),
         0,
         0.0f, 0.0f,
     };
+    init_pushconst_fastdiv(pc);
     ggml_vk_sync_buffers(subctx);
     ggml_vk_dispatch_pipeline(ctx, subctx, pipeline, { in, out }, sizeof(vk_op_unary_push_constants), &pc, elements);
 }
@@ -4096,7 +4135,7 @@ static bool ggml_vk_op_supports_incontiguous(ggml_op op) {
 }
 
 template<typename PC>
-static void ggml_vk_op_f32(ggml_backend_vk_context * ctx, vk_context& subctx, const ggml_tensor * src0, const ggml_tensor * src1, const ggml_tensor * src2, ggml_tensor * dst, ggml_op op, const PC&& pc, bool dryrun = false) {
+static void ggml_vk_op_f32(ggml_backend_vk_context * ctx, vk_context& subctx, const ggml_tensor * src0, const ggml_tensor * src1, const ggml_tensor * src2, ggml_tensor * dst, ggml_op op, PC&& pc, bool dryrun = false) {
     VK_LOG_DEBUG("ggml_vk_op_f32((" << src0 << ", name=" << src0->name << ", type=" << src0->type << ", ne0=" << src0->ne[0] << ", ne1=" << src0->ne[1] << ", ne2=" << src0->ne[2] << ", ne3=" << src0->ne[3] << ", nb0=" << src0->nb[0] << ", nb1=" << src0->nb[1] << ", nb2=" << src0->nb[2] << ", nb3=" << src0->nb[3];
     if (src1 != nullptr) {
         std::cerr << "), (" << src1 << ", name=" << src1->name << ", type=" << src1->type << ", ne0=" << src1->ne[0] << ", ne1=" << src1->ne[1] << ", ne2=" << src1->ne[2] << ", ne3=" << src1->ne[3] << ", nb0=" << src1->nb[0] << ", nb1=" << src1->nb[1] << ", nb2=" << src1->nb[2] << ", nb3=" << src1->nb[3];
@@ -4136,6 +4175,8 @@ static void ggml_vk_op_f32(ggml_backend_vk_context * ctx, vk_context& subctx, co
     const uint64_t ned3 = dst->ne[3];
     const uint64_t ned = ned0 * ned1;
 
+    init_pushconst_fastdiv(pc);
+
     vk_pipeline pipeline = ggml_vk_op_get_pipeline(ctx, src0, src1, src2, dst, op);
 
     if (pipeline == nullptr) {

ggml/src/ggml-vulkan/vulkan-shaders/generic_unary_head.comp

@@ -8,6 +8,13 @@ layout (push_constant) uniform parameter
     uint ne10; uint ne11; uint ne12; uint ne13; uint nb10; uint nb11; uint nb12; uint nb13;
     uint d_offset;
     float param1; float param2;
+
+    uint ne0_012mp; uint ne0_012L;
+    uint ne0_01mp;  uint ne0_01L;
+    uint ne0_0mp;   uint ne0_0L;
+    uint ne1_012mp; uint ne1_012L;
+    uint ne1_01mp;  uint ne1_01L;
+    uint ne1_0mp;   uint ne1_0L;
 } p;
 
 layout (binding = 0) readonly buffer A {A_TYPE data_a[];};
@@ -17,22 +24,30 @@ uint get_idx() {
     return gl_GlobalInvocationID.z * 262144 + gl_GlobalInvocationID.y * 512 + gl_GlobalInvocationID.x;
 }
 
+// see init_fastdiv_values in ggml-vulkan.cpp
+uint fastdiv(uint n, uint mp, uint L) {
+    uint msbs, lsbs;
+    // msbs = mulhi(n, mp)
+    umulExtended(n, mp, msbs, lsbs);
+    return (msbs + n) >> L;
+}
+
 uint src0_idx(uint idx) {
-    const uint i03 = idx / (p.ne02*p.ne01*p.ne00);
+    const uint i03 = fastdiv(idx, p.ne0_012mp, p.ne0_012L);
     const uint i03_offset = i03 * p.ne02*p.ne01*p.ne00;
-    const uint i02 = (idx - i03_offset) / (p.ne01*p.ne00);
+    const uint i02 = fastdiv(idx - i03_offset, p.ne0_01mp, p.ne0_01L);
     const uint i02_offset = i02*p.ne01*p.ne00;
-    const uint i01 = (idx - i03_offset - i02_offset) / p.ne00;
+    const uint i01 = fastdiv(idx - i03_offset - i02_offset, p.ne0_0mp, p.ne0_0L);
     const uint i00 = idx - i03_offset - i02_offset - i01*p.ne00;
     return i03*p.nb03 + i02*p.nb02 + i01*p.nb01 + i00*p.nb00;
 }
 
 uint dst_idx(uint idx) {
-    const uint i13 = idx / (p.ne12*p.ne11*p.ne10);
+    const uint i13 = fastdiv(idx, p.ne1_012mp, p.ne1_012L);
     const uint i13_offset = i13 * p.ne12*p.ne11*p.ne10;
-    const uint i12 = (idx - i13_offset) / (p.ne11*p.ne10);
+    const uint i12 = fastdiv(idx - i13_offset, p.ne1_01mp, p.ne1_01L);
     const uint i12_offset = i12*p.ne11*p.ne10;
-    const uint i11 = (idx - i13_offset - i12_offset) / p.ne10;
+    const uint i11 = fastdiv(idx - i13_offset - i12_offset, p.ne1_0mp, p.ne1_0L);
     const uint i10 = idx - i13_offset - i12_offset - i11*p.ne10;
     return i13*p.nb13 + i12*p.nb12 + i11*p.nb11 + i10*p.nb10;
 }

tests/test-backend-ops.cpp

@@ -3861,6 +3861,8 @@ static std::vector<std::unique_ptr<test_case>> make_test_cases_perf() {
     test_cases.emplace_back(new test_bin_bcast(ggml_add, GGML_TYPE_F32, {4096, 1, 1, 1}, {1, 512, 1, 1}));
 
     test_cases.emplace_back(new test_cpy(GGML_TYPE_F32, GGML_TYPE_F16, {512, 3072, 1, 1}));
+    test_cases.emplace_back(new test_cpy(GGML_TYPE_F32, GGML_TYPE_F32, {8192, 512, 2, 1}, {0, 2, 1, 3}));
+    test_cases.emplace_back(new test_cpy(GGML_TYPE_F32, GGML_TYPE_F32, {3072, 512, 2, 1}, {0, 2, 1, 3}));
 
     test_cases.emplace_back(new test_soft_max(GGML_TYPE_F32, {4096, 4096, 5, 1}, false, 1.0f, 0.0f));
     test_cases.emplace_back(new test_soft_max(GGML_TYPE_F32, {77, 4096, 5, 1}, false, 1.0f, 0.0f));