CUDA: compute fast hash instead of expensive props check

Author: am17an

ggml/src/ggml-cuda/common.cuh

@@ -1186,6 +1186,8 @@ struct ggml_cuda_graph {
     std::vector<cudaGraphNode_t> nodes;
     bool disable_due_to_gpu_arch = false;
     bool warmup_complete = false;
+    uint64_t last_props_hash = 0;  // FNV hash of node properties from last successful check
+    int      props_stable = 0;     // consecutive checks with no change
     std::vector<ggml_cuda_graph_node_properties> props;
 
     // these are extra tensors (inputs) that participate in the ggml graph but are not nodes

ggml/src/ggml-cuda/ggml-cuda.cu

@@ -3041,12 +3041,48 @@ static const void * ggml_cuda_graph_get_key(ggml_cgraph * cgraph) {
     return cgraph->nodes[0];
 }
 
+//compute a FNV-1a over all nodes and srcs which should change when a cuda graph cannot be reused
+static uint64_t ggml_cuda_graph_hash(ggml_cgraph * cgraph) {
+    uint64_t h = 0xcbf29ce484222325ULL;
+    constexpr uint64_t prime = 0x100000001b3ULL;
+
+    for (int i = 0; i < cgraph->n_nodes; i++) {
+        const ggml_tensor * node = cgraph->nodes[i];
+
+        h ^= (uintptr_t)node->data;
+        h *= prime;
+
+        for (int s = 0; s < GGML_MAX_SRC; s++) {
+            if (node->src[s]) {
+                h ^= (uintptr_t)node->src[s]->data;
+                h *= prime;
+            }
+        }
+
+        // Hash first 16 bytes of op_params
+        const uint64_t * params = (const uint64_t *)node->op_params;
+        h ^= params[0];
+        h *= prime;
+        h ^= params[1];
+        h *= prime;
+    }
+
+    return h;
+}
+
 static bool ggml_cuda_graph_update_required(ggml_backend_cuda_context * cuda_ctx, ggml_cgraph * cgraph) {
     bool res = false;
 
     const void * graph_key = ggml_cuda_graph_get_key(cgraph);
     ggml_cuda_graph * graph = cuda_ctx->cuda_graph(graph_key);
 
+    if (graph->props_stable >= 2 && graph->props.size() == (size_t)cgraph->n_nodes) {
+        if (ggml_cuda_graph_hash(cgraph) == graph->last_props_hash) {
+            return false;
+        }
+        graph->props_stable = 0;
+    }
+
     // Check if the graph size has changed
     if (graph->props.size() != (size_t)cgraph->n_nodes) {
         res = true;
@@ -3096,6 +3132,13 @@ static bool ggml_cuda_graph_update_required(ggml_backend_cuda_context * cuda_ctx
         ggml_cuda_graph_node_set_properties(&graph->extra[i], srcs_extra[i]);
     }
 
+    if (!res) {
+        graph->props_stable++;
+        graph->last_props_hash = ggml_cuda_graph_hash(cgraph);
+    } else {
+        graph->props_stable = 0;
+    }
+
     return res;
 }