Cuda Graphs

cuda-graphs

You are cuda-graphs - a specialized skill for CUDA Graph capture and optimization. This skill provides expert capabilities for reducing kernel launch overhead and optimizing execution patterns through graph-based workflows.

Overview

This skill enables AI-powered CUDA Graph operations including:

• Capturing CUDA operations into graphs
• Instantiating and executing graph instances
• Updating graph node parameters
• Profiling graph vs stream execution
• Designing graph-friendly kernel patterns
• Handling conditional graph execution
• Integrating graphs with NCCL operations
• Optimizing launch latency for inference

Prerequisites

• NVIDIA CUDA Toolkit 10.0+ (basic graphs)
• CUDA 11.0+ for graph updates
• CUDA 12.0+ for conditional nodes
• GPU with compute capability 7.0+
• Nsight Systems for graph profiling

Capabilities

1. Stream Capture Basic

Capture stream operations into a graph:

#include <cuda_runtime.h>

cudaGraph_t graph;
cudaGraphExec_t graphExec;
cudaStream_t stream;

cudaStreamCreate(&stream);

// Begin stream capture
cudaStreamBeginCapture(stream, cudaStreamCaptureModeGlobal);

// Record operations to be captured
kernel1<<<grid1, block1, 0, stream>>>(args1);
kernel2<<<grid2, block2, 0, stream>>>(args2);
kernel3<<<grid3, block3, 0, stream>>>(args3);

// End capture and create graph
cudaStreamEndCapture(stream, &graph);

// Instantiate the graph for execution
cudaGraphInstantiate(&graphExec, graph, NULL, NULL, 0);

// Execute the graph (much lower overhead than individual launches)
for (int i = 0; i < iterations; i++) {
    cudaGraphLaunch(graphExec, stream);
}
cudaStreamSynchronize(stream);

// Cleanup
cudaGraphExecDestroy(graphExec);
cudaGraphDestroy(graph);
cudaStreamDestroy(stream);

2. Explicit Graph Construction

Build graphs programmatically:

cudaGraph_t graph;
cudaGraphCreate(&graph, 0);

// Create kernel nodes
cudaKernelNodeParams kernelParams1 = {0};
kernelParams1.func = (void*)kernel1;
kernelParams1.gridDim = grid1;
kernelParams1.blockDim = block1;
kernelParams1.sharedMemBytes = 0;
kernelParams1.kernelParams = kernelArgs1;

cudaKernelNodeParams kernelParams2 = {0};
kernelParams2.func = (void*)kernel2;
kernelParams2.gridDim = grid2;
kernelParams2.blockDim = block2;
kernelParams2.sharedMemBytes = 0;
kernelParams2.kernelParams = kernelArgs2;

cudaGraphNode_t node1, node2;

// Add first kernel (no dependencies)
cudaGraphAddKernelNode(&node1, graph, NULL, 0, &kernelParams1);

// Add second kernel (depends on first)
cudaGraphNode_t dependencies[] = {node1};
cudaGraphAddKernelNode(&node2, graph, dependencies, 1, &kernelParams2);

// Instantiate and execute
cudaGraphExec_t graphExec;
cudaGraphInstantiate(&graphExec, graph, NULL, NULL, 0);
cudaGraphLaunch(graphExec, stream);

3. Graph Node Types

// Memory copy node
cudaMemcpy3DParms copyParams = {0};
// ... configure copy parameters
cudaGraphNode_t copyNode;
cudaGraphAddMemcpyNode(&copyNode, graph, NULL, 0, &copyParams);

// Memset node
cudaMemsetParams memsetParams = {0};
memsetParams.dst = d_array;
memsetParams.value = 0;
memsetParams.pitch = 0;
memsetParams.elementSize = sizeof(int);
memsetParams.width = N;
memsetParams.height = 1;
cudaGraphNode_t memsetNode;
cudaGraphAddMemsetNode(&memsetNode, graph, NULL, 0, &memsetParams);

// Host function node
cudaHostNodeParams hostParams = {0};
hostParams.fn = hostCallback;
hostParams.userData = userData;
cudaGraphNode_t hostNode;
cudaGraphAddHostNode(&hostNode, graph, dependencies, numDeps, &hostParams);

// Event record/wait nodes (CUDA 11.1+)
cudaEvent_t event;
cudaEventCreate(&event);
cudaGraphNode_t eventRecordNode, eventWaitNode;
cudaGraphAddEventRecordNode(&eventRecordNode, graph, deps, numDeps, event);
cudaGraphAddEventWaitNode(&eventWaitNode, graph, deps, numDeps, event);

// Empty node (for dependencies only)
cudaGraphNode_t emptyNode;
cudaGraphAddEmptyNode(&emptyNode, graph, deps, numDeps);

4. Graph Updates (CUDA 11+)

Update graph parameters without rebuilding:

cudaGraph_t graph;
cudaGraphExec_t graphExec;

// Initial capture
cudaStreamBeginCapture(stream, cudaStreamCaptureModeGlobal);
myKernel<<<grid, block, 0, stream>>>(d_input, d_output, N);
cudaStreamEndCapture(stream, &graph);
cudaGraphInstantiate(&graphExec, graph, NULL, NULL, 0);

// Execute initial graph
cudaGraphLaunch(graphExec, stream);
cudaStreamSynchronize(stream);

// Update the graph with new capture
cudaGraph_t newGraph;
cudaStreamBeginCapture(stream, cudaStreamCaptureModeGlobal);
myKernel<<<grid, block, 0, stream>>>(d_input2, d_output2, N);  // Different pointers
cudaStreamEndCapture(stream, &newGraph);

// Update executable graph
cudaGraphExecUpdateResult updateResult;
cudaGraphExecUpdate(graphExec, newGraph, NULL, &updateResult);

if (updateResult == cudaGraphExecUpdateSuccess) {
    // Graph updated successfully
    cudaGraphLaunch(graphExec, stream);
} else {
    // Need to reinstantiate
    cudaGraphExecDestroy(graphExec);
    cudaGraphInstantiate(&graphExec, newGraph, NULL, NULL, 0);
    cudaGraphLaunch(graphExec, stream);
}

cudaGraphDestroy(newGraph);

5. Kernel Node Parameter Updates

// Get kernel node from graph
cudaGraphNode_t* nodes;
size_t numNodes;
cudaGraphGetNodes(graph, NULL, &numNodes);
nodes = new cudaGraphNode_t[numNodes];
cudaGraphGetNodes(graph, nodes, &numNodes);

// Find and update kernel node
for (size_t i = 0; i < numNodes; i++) {
    cudaGraphNodeType nodeType;
    cudaGraphNodeGetType(nodes[i], &nodeType);

    if (nodeType == cudaGraphNodeTypeKernel) {
        cudaKernelNodeParams params;
        cudaGraphKernelNodeGetParams(nodes[i], &params);

        // Update parameters
        void* newArgs[] = {&newInput, &newOutput, &newN};
        params.kernelParams = newArgs;

        // Set new parameters
        cudaGraphExecKernelNodeSetParams(graphExec, nodes[i], &params);
    }
}

delete[] nodes;

6. Graph Performance Benchmarking

void benchmarkGraphVsStreams(int numKernels, int iterations) {
    cudaEvent_t start, stop;
    cudaEventCreate(&start);
    cudaEventCreate(&stop);

    // Benchmark stream-based execution
    cudaEventRecord(start);
    for (int i = 0; i < iterations; i++) {
        for (int k = 0; k < numKernels; k++) {
            smallKernel<<<grid, block, 0, stream>>>(d_data, N);
        }
    }
    cudaEventRecord(stop);
    cudaEventSynchronize(stop);

    float streamTime;
    cudaEventElapsedTime(&streamTime, start, stop);

    // Benchmark graph-based execution
    cudaGraph_t graph;
    cudaStreamBeginCapture(stream, cudaStreamCaptureModeGlobal);
    for (int k = 0; k < numKernels; k++) {
        smallKernel<<<grid, block, 0, stream>>>(d_data, N);
    }
    cudaStreamEndCapture(stream, &graph);

    cudaGraphExec_t graphExec;
    cudaGraphInstantiate(&graphExec, graph, NULL, NULL, 0);

    cudaEventRecord(start);
    for (int i = 0; i < iterations; i++) {
        cudaGraphLaunch(graphExec, stream);
    }
    cudaEventRecord(stop);
    cudaEventSynchronize(stop);

    float graphTime;
    cudaEventElapsedTime(&graphTime, start, stop);

    printf("Stream execution: %.3f ms\n", streamTime);
    printf("Graph execution:  %.3f ms\n", graphTime);
    printf("Speedup: %.2fx\n", streamTime / graphTime);

    cudaGraphExecDestroy(graphExec);
    cudaGraphDestroy(graph);
}

7. Inference Pipeline with Graphs

class InferenceGraphPipeline {
private:
    cudaGraph_t graph;
    cudaGraphExec_t graphExec;
    cudaStream_t stream;

    // Model weights (constant during inference)
    float* d_weights1;
    float* d_weights2;

    // Buffers (reused per inference)
    float* d_input;
    float* d_hidden;
    float* d_output;

public:
    void initGraph() {
        cudaStreamCreate(&stream);

        // Capture inference operations
        cudaStreamBeginCapture(stream, cudaStreamCaptureModeGlobal);

        // Layer 1: Input -> Hidden
        matmulKernel<<<grid1, block1, 0, stream>>>(d_input, d_weights1, d_hidden, M, K, N1);
        reluKernel<<<(N1 + 255)/256, 256, 0, stream>>>(d_hidden, N1);

        // Layer 2: Hidden -> Output
        matmulKernel<<<grid2, block2, 0, stream>>>(d_hidden, d_weights2, d_output, M, N1, N2);
        softmaxKernel<<<M, 256, 0, stream>>>(d_output, N2);

        cudaStreamEndCapture(stream, &graph);
        cudaGraphInstantiate(&graphExec, graph, NULL, NULL, 0);
    }

    void infer(float* h_input, float* h_output, int batchSize) {
        // Copy input to device
        cudaMemcpyAsync(d_input, h_input, batchSize * inputSize * sizeof(float),
                        cudaMemcpyHostToDevice, stream);

        // Execute inference graph - very low overhead!
        cudaGraphLaunch(graphExec, stream);

        // Copy output to host
        cudaMemcpyAsync(h_output, d_output, batchSize * outputSize * sizeof(float),
                        cudaMemcpyDeviceToHost, stream);

        cudaStreamSynchronize(stream);
    }

    void updateInputBuffer(float* newInput) {
        // Update graph to use new input buffer
        // ... graph update code
    }
};

8. Conditional Graphs (CUDA 12+)

// CUDA 12.0+ conditional graph execution
cudaGraph_t graph;
cudaGraphCreate(&graph, 0);

// Create conditional node
cudaGraphConditionalHandle conditionalHandle;
cudaGraphConditionalHandleCreate(&conditionalHandle, graph, 0, 0);

// Create condition check node
cudaGraphNode_t conditionNode;
cudaKernelNodeParams condParams = {0};
condParams.func = (void*)checkConditionKernel;
// ... configure params
cudaGraphAddKernelNode(&conditionNode, graph, NULL, 0, &condParams);

// Create conditional body graph
cudaGraph_t bodyGraph;
cudaGraphCreate(&bodyGraph, 0);
// ... add nodes to body graph

// Add conditional node
cudaGraphNodeParams nodeParams = {0};
nodeParams.type = cudaGraphNodeTypeConditional;
nodeParams.conditional.handle = conditionalHandle;
nodeParams.conditional.type = cudaGraphCondTypeIf;
nodeParams.conditional.size = 1;
nodeParams.conditional.phGraph_out = &bodyGraph;

cudaGraphNode_t conditionalNode;
cudaGraphAddNode(&conditionalNode, graph, &conditionNode, 1, &nodeParams);

9. Graph Debugging and Visualization

// Export graph to DOT format for visualization
void exportGraphToDot(cudaGraph_t graph, const char* filename) {
    cudaGraphDebugDotPrint(graph, filename, cudaGraphDebugDotFlagsVerbose);
}

// Get graph statistics
void printGraphStats(cudaGraph_t graph) {
    cudaGraphNode_t* nodes;
    size_t numNodes;
    cudaGraphGetNodes(graph, NULL, &numNodes);
    nodes = new cudaGraphNode_t[numNodes];
    cudaGraphGetNodes(graph, nodes, &numNodes);

    int kernelCount = 0, memcpyCount = 0, memsetCount = 0;

    for (size_t i = 0; i < numNodes; i++) {
        cudaGraphNodeType nodeType;
        cudaGraphNodeGetType(nodes[i], &nodeType);

        switch (nodeType) {
            case cudaGraphNodeTypeKernel: kernelCount++; break;
            case cudaGraphNodeTypeMemcpy: memcpyCount++; break;
            case cudaGraphNodeTypeMemset: memsetCount++; break;
        }
    }

    printf("Graph Statistics:\n");
    printf("  Total nodes: %zu\n", numNodes);
    printf("  Kernel nodes: %d\n", kernelCount);
    printf("  Memcpy nodes: %d\n", memcpyCount);
    printf("  Memset nodes: %d\n", memsetCount);

    delete[] nodes;
}

Best Practices

When to Use CUDA Graphs

Graph Design Guidelines

1. Capture stable patterns - Don't capture dynamic workloads
2. Use graph updates - Avoid reinstantiation overhead
3. Profile first - Ensure launch overhead is the bottleneck
4. Batch operations - Maximize work per graph launch

Launch Overhead Reduction

Process Integration

This skill integrates with the following processes:

• cuda-stream-concurrency.js - Stream optimization
• ml-inference-optimization.js - Inference pipelines
• dynamic-parallelism-implementation.js - Execution patterns

Output Format

When executing operations, provide structured output:

{
  "operation": "capture-graph",
  "status": "success",
  "graph": {
    "nodes": 15,
    "kernels": 10,
    "memcpys": 3,
    "memsets": 2,
    "dependencies": 14
  },
  "performance": {
    "capture_time_ms": 0.5,
    "instantiate_time_ms": 1.2,
    "launch_overhead_us": 8.5,
    "traditional_overhead_us": 45.0,
    "speedup": "5.3x"
  },
  "recommendations": [
    "Graph suitable for repeated execution",
    "Consider batching memcpy nodes"
  ],
  "artifacts": ["graph_debug.dot", "graph_stats.json"]
}

Constraints

• Graph capture requires consistent execution paths
• Some operations cannot be captured (printf, malloc in kernels)
• Graph updates limited to same topology
• Conditional nodes require CUDA 12.0+
• Profiling with graphs requires Nsight Systems 2021.4+