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<div class="bd-toc-item navbar-nav"><p aria-level="2" class="caption" role="heading"><span class="caption-text">Getting Started</span></p>
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<li class="toctree-l1"><a class="reference internal" href="../overview.html">Overview</a></li>
<li class="toctree-l1"><a class="reference internal" href="../quick-start-guide.html">Quick Start Guide</a></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../installation/index.html">Installation</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../installation/containers.html">Pre-built release container images on NGC</a></li>
<li class="toctree-l2"><a class="reference internal" href="../installation/linux.html">Installing on Linux via <code class="docutils literal notranslate"><span class="pre">pip</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="../installation/build-from-source-linux.html">Building from Source Code on Linux</a></li>
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<p aria-level="2" class="caption" role="heading"><span class="caption-text">Deployment Guide</span></p>
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<li class="toctree-l1 has-children"><a class="reference internal" href="../examples/llm_api_examples.html">LLM Examples</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_inference.html">Generate text</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_inference_async.html">Generate text asynchronously</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_inference_async_streaming.html">Generate text in streaming</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_inference_distributed.html">Distributed LLM Generation</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_guided_decoding.html">Generate text with guided decoding</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_logits_processor.html">Control generated text using logits processor</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_multilora.html">Generate text with multiple LoRA adapters</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_sparse_attention.html">Sparse Attention</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_speculative_decoding.html">Speculative Decoding</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_kv_cache_connector.html">KV Cache Connector</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_kv_cache_offloading.html">KV Cache Offloading</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_runtime.html">Runtime Configuration Examples</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_sampling.html">Sampling Techniques Showcase</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_mgmn_llm_distributed.html">Run LLM-API with pytorch backend on Slurm</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_mgmn_trtllm_bench.html">Run trtllm-bench with pytorch backend on Slurm</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/llm_mgmn_trtllm_serve.html">Run trtllm-serve with pytorch backend on Slurm</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../examples/trtllm_serve_examples.html">Online Serving Examples</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../examples/curl_chat_client.html">Curl Chat Client</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/curl_chat_client_for_multimodal.html">Curl Chat Client For Multimodal</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/curl_completion_client.html">Curl Completion Client</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/deepseek_r1_reasoning_parser.html">Deepseek R1 Reasoning Parser</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/genai_perf_client.html">Genai Perf Client</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/genai_perf_client_for_multimodal.html">Genai Perf Client For Multimodal</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/openai_chat_client.html">OpenAI Chat Client</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/openai_chat_client_for_multimodal.html">OpenAI Chat Client for Multimodal</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/openai_completion_client.html">OpenAI Completion Client</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/openai_completion_client_for_lora.html">Openai Completion Client For Lora</a></li>
<li class="toctree-l2"><a class="reference internal" href="../examples/openai_completion_client_json_schema.html">OpenAI Completion Client with JSON Schema</a></li>
</ul>
</details></li>
<li class="toctree-l1"><a class="reference internal" href="../examples/dynamo_k8s_example.html">Dynamo K8s Example</a></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="../deployment-guide/index.html">Model Recipes</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-deepseek-r1-on-trtllm.html">Deployment Guide for DeepSeek R1 on TensorRT LLM - Blackwell &amp; Hopper Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-llama3.3-70b-on-trtllm.html">Deployment Guide for Llama3.3 70B on TensorRT LLM - Blackwell &amp; Hopper Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-llama4-scout-on-trtllm.html">Deployment Guide for Llama4 Scout 17B on TensorRT LLM - Blackwell &amp; Hopper Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-gpt-oss-on-trtllm.html">Deployment Guide for GPT-OSS on TensorRT-LLM - Blackwell Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-qwen3-on-trtllm.html">Deployment Guide for Qwen3 on TensorRT LLM - Blackwell &amp; Hopper Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-qwen3-next-on-trtllm.html">Deployment Guide for Qwen3 Next on TensorRT LLM - Blackwell &amp; Hopper Hardware</a></li>
<li class="toctree-l2"><a class="reference internal" href="../deployment-guide/deployment-guide-for-kimi-k2-thinking-on-trtllm.html">Deployment Guide for Kimi K2 Thinking on TensorRT LLM - Blackwell</a></li>
</ul>
</details></li>
</ul>
<p aria-level="2" class="caption" role="heading"><span class="caption-text">Models</span></p>
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<li class="toctree-l1"><a class="reference internal" href="../models/adding-new-model.html">Adding a New Model</a></li>
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<p aria-level="2" class="caption" role="heading"><span class="caption-text">CLI Reference</span></p>
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<li class="toctree-l1"><a class="reference internal" href="../commands/trtllm-bench.html">trtllm-bench</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../commands/trtllm-serve/run-benchmark-with-trtllm-serve.html">Run benchmarking with <code class="docutils literal notranslate"><span class="pre">trtllm-serve</span></code></a></li>
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</details></li>
</ul>
<p aria-level="2" class="caption" role="heading"><span class="caption-text">API Reference</span></p>
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<li class="toctree-l1"><a class="reference internal" href="../llm-api/index.html">LLM API Introduction</a></li>
<li class="toctree-l1"><a class="reference internal" href="../llm-api/reference.html">API Reference</a></li>
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<p aria-level="2" class="caption" role="heading"><span class="caption-text">Features</span></p>
<ul class="nav bd-sidenav">
<li class="toctree-l1"><a class="reference internal" href="../features/feature-combination-matrix.html">Feature Combination Matrix</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/attention.html">Multi-Head, Multi-Query, and Group-Query Attention</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/disagg-serving.html">Disaggregated Serving</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/kvcache.html">KV Cache System</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/long-sequence.html">Long Sequences</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/lora.html">LoRA (Low-Rank Adaptation)</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/multi-modality.html">Multimodal Support in TensorRT LLM</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/overlap-scheduler.html">Overlap Scheduler</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/paged-attention-ifb-scheduler.html">Paged Attention, IFB, and Request Scheduling</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/parallel-strategy.html">Parallelism in TensorRT LLM</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/quantization.html">Quantization</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/sampling.html">Sampling</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/additional-outputs.html">Additional Outputs</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/guided-decoding.html">Guided Decoding</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/speculative-decoding.html">Speculative Decoding</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/checkpoint-loading.html">Checkpoint Loading</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/auto_deploy/auto-deploy.html">AutoDeploy (Prototype)</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/ray-orchestrator.html">Ray Orchestrator (Prototype)</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/torch_compile_and_piecewise_cuda_graph.html">Torch Compile &amp; Piecewise CUDA Graph</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/helix.html">Helix Parallelism</a></li>
<li class="toctree-l1"><a class="reference internal" href="../features/kv-cache-connector.html">KV Cache Connector</a></li>
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<p aria-level="2" class="caption" role="heading"><span class="caption-text">Developer Guide</span></p>
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<li class="toctree-l1"><a class="reference internal" href="../developer-guide/overview.html">Architecture Overview</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/perf-analysis.html">Performance Analysis</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/perf-benchmarking.html">TensorRT LLM Benchmarking</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/ci-overview.html">Continuous Integration Overview</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/dev-containers.html">Using Dev Containers</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/api-change.html">LLM API Change Guide</a></li>
<li class="toctree-l1"><a class="reference internal" href="../developer-guide/kv-transfer.html">Introduction to KV Cache Transmission</a></li>
</ul>
<p aria-level="2" class="caption" role="heading"><span class="caption-text">Blogs</span></p>
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<section class="tex2jax_ignore mathjax_ignore" id="kv-cache-manager">
<h1>KV Cache Manager<a class="headerlink" href="#kv-cache-manager" title="Link to this heading">#</a></h1>
<p>In Transformer-based models, the KV (Key-Value) Cache is a mechanism used to optimize decoding efficiency, particularly during autoregressive generation tasks.
Since KV Cache requires memory to store, it is also an important resource.
In TensorRT LLM, KV Cache is managed by the <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code>.</p>
<p>For details of the TensorRT LLM <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code> implementation see <a class="reference internal" href="#../advanced/kv-cache-management.md"><span class="xref myst">KV Cache Management</span></a>.</p>
<section id="kv-cache-manager-introduction">
<h2>KV Cache Manager Introduction<a class="headerlink" href="#kv-cache-manager-introduction" title="Link to this heading">#</a></h2>
<p><code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code> is a type of resource manager, inheriting from <code class="docutils literal notranslate"><span class="pre">BaseResourceManager</span></code>.
Therefore, it implements the interfaces declared by <code class="docutils literal notranslate"><span class="pre">BaseResourceManager</span></code>.</p>
<p>Note: As the project evolves, these interfaces may change.</p>
</section>
<section id="interfaces">
<h2>Interfaces<a class="headerlink" href="#interfaces" title="Link to this heading">#</a></h2>
<p>The interfaces from <code class="docutils literal notranslate"><span class="pre">BaseResourceManager</span></code> include:</p>
<ul class="simple">
<li><p><strong>prepare_resources</strong>: Called at each step before model forward in <code class="docutils literal notranslate"><span class="pre">PyExecutor</span></code> for the current batch.
In <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code>, this involves allocating KV Cache memory. This allocation varies depending on the request type.
For requests entering the context phase for the first time, KV Cache needs to be allocated for the entire context.
For requests already in the generation phase, KV Cache is allocated for the upcoming step.
If KV Cache is organized in blocks and free space is available within a block, actual allocation may not occur.</p></li>
<li><p><strong>update_resources</strong>: Called at the end of each step for the current batch to update allocated resources.
For KV Cache, updates may not be necessary, so this function currently performs no operations.
If KV Cache reuse is supported in Python, updates like KV Cache Radix Tree management occurs here.</p></li>
<li><p><strong>free_resources</strong>: Called when a request finishes to free the resources allocated for that request.
For KV Cache, if reuse is not enabled, the KV Cache memory used by the request should be recycled.
In the C++ binding implementation, this might involve calling the bindings <code class="docutils literal notranslate"><span class="pre">remove_sequence</span></code> method to free the KV Cache memory related to that request.</p></li>
</ul>
<p>There are also two interfaces designed for <code class="docutils literal notranslate"><span class="pre">CapacityScheduler</span></code>:</p>
<ul class="simple">
<li><p><strong>get_max_resource_count</strong>: Queries the maximum number of resources available. For <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code>, this is usually the maximum number of KV Cache blocks.</p></li>
<li><p><strong>get_needed_resource_to_completion</strong>: Computes the resources needed for a single request to complete.
<code class="docutils literal notranslate"><span class="pre">CapacityScheduler</span></code> uses this to sum up the total resources needed and determine if new requests can be accommodated.</p></li>
</ul>
<p>In addition to the <code class="docutils literal notranslate"><span class="pre">BaseResourceManager</span></code> interfaces, <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code> has interfaces related to the <code class="docutils literal notranslate"><span class="pre">ModelEngine</span></code> in use.
For <code class="docutils literal notranslate"><span class="pre">PyTorchModelEngine</span></code>, common interfaces include:</p>
<ul class="simple">
<li><p><strong>get_batch_cache_indices</strong>: Takes a list of <code class="docutils literal notranslate"><span class="pre">LlmRequest</span></code> and returns a <code class="docutils literal notranslate"><span class="pre">Dict[List[int]]</span></code>, indicating the block IDs for each request.</p></li>
<li><p><strong>get_buffers</strong>: Returns the buffer of the KV Cache pool for a given layer, used by the attention backend. The shape might be [<code class="docutils literal notranslate"><span class="pre">num_blocks</span></code>, 2, <code class="docutils literal notranslate"><span class="pre">num_tokens_per_block</span></code>, <code class="docutils literal notranslate"><span class="pre">num_kv_heads</span></code>, <code class="docutils literal notranslate"><span class="pre">head_dim</span></code>].</p></li>
<li><p><strong>get_num_free_blocks</strong>: Returns the number of free blocks available for allocation.</p></li>
</ul>
<p>There are also interfaces for warming up <code class="docutils literal notranslate"><span class="pre">PyTorchModelEngine</span></code>, especially when using CUDA graphs:</p>
<ul class="simple">
<li><p><strong>add_padding_request</strong>: Adds a sequence of context length 1 to KV Cache as a warmup request.
This is optional if CUDA Graph is not used in your proof of concept.</p></li>
</ul>
</section>
<section id="customize-kv-cache-manager">
<h2>Customize KV Cache Manager<a class="headerlink" href="#customize-kv-cache-manager" title="Link to this heading">#</a></h2>
<p>To customize <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code>, implement all the necessary interfaces.
Then, integrate it into the <code class="docutils literal notranslate"><span class="pre">PyExecutor</span></code>. For the PyTorch backend, the relevant code is in <a class="reference internal" href="#../../../tensorrt_llm/_torch/pyexecutor/backend_registries/pytorch_model_registry.py"><span class="xref myst">pytorch_model_registry.py</span></a>.
In the <code class="docutils literal notranslate"><span class="pre">create_pytorch_model_based_executor</span></code> function, the <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code> is instantiated as follows:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span> <span class="n">kv_cache_manager</span> <span class="o">=</span> <span class="n">KVCacheManager</span><span class="p">(</span>
<span class="n">executor_config</span><span class="o">.</span><span class="n">kv_cache_config</span><span class="p">,</span>
<span class="n">tensorrt_llm</span><span class="o">.</span><span class="n">bindings</span><span class="o">.</span><span class="n">internal</span><span class="o">.</span><span class="n">batch_manager</span><span class="o">.</span><span class="n">CacheType</span><span class="o">.</span><span class="n">SELF</span><span class="p">,</span>
<span class="n">num_layers</span><span class="o">=</span><span class="n">model_engine</span><span class="o">.</span><span class="n">model</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">num_hidden_layers</span><span class="p">,</span>
<span class="n">num_kv_heads</span><span class="o">=</span><span class="n">model_engine</span><span class="o">.</span><span class="n">model</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">num_key_value_heads</span><span class="p">,</span>
<span class="n">head_dim</span><span class="o">=</span><span class="n">head_dim</span><span class="p">,</span>
<span class="n">tokens_per_block</span><span class="o">=</span><span class="n">tokens_per_block</span><span class="p">,</span>
<span class="n">max_seq_len</span><span class="o">=</span><span class="n">max_seq_len</span><span class="p">,</span>
<span class="n">max_batch_size</span><span class="o">=</span><span class="n">max_num_requests</span><span class="p">,</span>
<span class="n">mapping</span><span class="o">=</span><span class="n">mapping</span><span class="p">,</span>
<span class="n">dtype</span><span class="o">=</span><span class="n">kv_cache_dtype</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>For local testing or proof of concept, update these lines to use your implementation.
Then, test it to ensure the <code class="docutils literal notranslate"><span class="pre">PyExecutor</span></code> runs with your customized <code class="docutils literal notranslate"><span class="pre">KVCacheManager</span></code>.</p>
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