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Running LLMs inside your Vespa application

Please refer to Large Language Models in Vespa for an introduction to using LLMs in Vespa.

Vespa supports evaluating LLMs within your application, both on CPU and GPU.

Note: Note that this is currently a Beta feature so changes can be expected.

Running large language models (LLMs) directly in your Vespa application offers various advantages, particularly in terms of data security and privacy. By running LLMs locally, sensitive information remains within the confines of the application or network, eliminating the risks associated with data transmission to external services. This is especially important for RAG use cases that handle sensitive or proprietary data, such as healthcare, finance, and legal services, where privacy compliance and data security are valid concerns.

Moreover, hosting LLMs locally allows applications to select from a wider range of models that best suit their specific needs, rather than being limited to the models offered by external providers. This flexibility enables businesses to optimize performance, cost, and efficiency tailored to their operational requirements. Additionally, managing LLMs in-house provides control over model versions, allowing companies to maintain stable and consistent outputs by choosing when and how to update their models.

Finally, while massively large foundation models dominates the generalist use case, the smaller, more specialized, models (sometimes called "small language models") have become much more capable.

For a quick start, check out the RAG sample app which demonstrates how to set up a local LLM.

Setting up LLM clients in services.xml

Note: This feature is available in Vespa versions >= 8.331

To set up the required inference engine for running your model, you need to define a LocalLLM component in your application's services.xml:

<services version="1.0">
  <container id="default" version="1.0">

    ...

    <component id="local" class="ai.vespa.llm.clients.LocalLLM">
      <config name="ai.vespa.llm.clients.llm-local-client">
          <model url="..." />
      </config>
    </component>

    ...

  </container>
</services>

This component will ensure that the underlying inference engine is started and load the model when the container nodes are started. Each container node in the cluster will load the LLM. Note that you can set up multiple clusters of container nodes. This can be helpful for instance if you have multiple LLMs that don't fit in the available GPU memory, or you would like to offload LLM inference to dedicated nodes for performance reasons.

The model configuration parameter can be either set to a known model-id for Vespa Cloud, a url or a path to the model inside the application package. Usually, however, LLM files are too large to practically be included in the application package, so the url attribute is used. See below for more information on model types that can be used in Vespa.

There are many other configuration parameters to customize how inference is run, please see the configuration section for more details.

Valid LLM models

Under the hood, Vespa uses llama.cpp. Any model file that works with llama.cpp can be used in Vespa. This includes the following base models and finetunes of them:

LLama 2/3
Mistral 7B
Mixtral MoE
Gemma
Command R+
Phi 2/3
And many more

Please refer to the supported models section of llama.cpp for a full list of updated models.

Vespa supports the GGUF file format. GGUF models can be found on HuggingFace, by searching for GGUF. Other LLM formats such safetensors and pytorch.bin models need to be converted GGUF before use. Please refer to llama.cpp for conversion tools.

Quantized models are also supported. Models are typically trained to FP16 precision, but GGUF files support reduced precision to 8-bit or lower. This can save space so larger models can fit in less memory. Be aware however, that inference time can increase when using reduced precision, so be sure to benchmark your application accordingly, both in token generation performance but also in terms of output quality.

Local LLM configuration

LLM model inference has a number of configuration parameters that is set in services.xml and are applied during model loading. There are also a set of parameters that can be set during inference which are passed as query parameters. Please refer below to inference parameters for more information on those.

The most significant model configuration parameters are:

model: the model file to use. The attributes are either model-id which specifies a known model in Vespa Cloud, url which specifies a URL to a model, for instance in HuggingFace, or path which specifies a file found in the application package.
parallelRequests: the maximum number of parallel requests to handle. This is the batch size of concurrent texts to generate.
contextSize: the size of context window. A model is typically trained with a given context size, but this can typically be increased if required. This setting has a direct impact on memory usage.
useGpu: toggle the use of GPU if available. Default is true, which means GPU will be used if it is found. See the GPU section below for more details.
gpuLayers : number of layers in the model to offload to GPU. This setting allows partial evaluation on CPU and GPU, so models larger than available GPU memory can be used. Default is to offload all layers to the GPU.
threads: the number of threads to use when using CPU only inference. The default is the number of available cores - 2. Do not set this higher than the core count, as this will severely impact performance.
maxTokens: the maximum number of tokens that will be generated. Default is
1. Overridden by corresponding inference parameter.

Please refer to the local LLM client configuration definition for an updated list of configuration parameters.

Some important points are worth considering here. First is the context window, given by the contextSize parameter, which is the size (in number of tokens) that the model uses to generate the next token. In general, larger context windows are required in RAG applications to hold the context from the retrieval stage. Models are trained with a certain context length, but this context length can typically be increased up to 4x without much loss in text generation quality.

The size of the context window has a direct impact on memory use. For instance, a typical 7B model such as Mistral 7B, with a size of 7 billion parameters will use around 14Gb memory when using FP16 precision, and 7Gb with 8-bit quantization. Assuming we use a 8-bit quantization:

A context window of 4096 will use 7.3Gb for the model, 512Mb for the context window and 296Mb for the compute buffer, requiring around 8Gb memory in total.
A context window of 32768 will use 7.3Gb for the model, 4Gb for the context window and 2.2Gb for the compute buffer, requiring almost 14Gb memory in total.

So, a single GPU with 16Gb memory can just about hold the 7B model with a context size of 32768. For reference, the Mistral 7B model is trained with this context size.

Now, when running in context of Vespa, we generally would like to handle multiple requests in parallel. The number of parallel requests we can handle per container node is set with the parallelRequests parameter. This in effect sets up a number of slots that can be evaluated simultaneously. Each sequence that should be generated requires a significant amount of memory to keep the context for each generated token.

The total amount of memory that is set for this task is given by the contextSize parameter. The effective context size for each request is this size divided by number of parallel requests. So, for a total context size of 32768 tokens and 10 parallel requests, each request effectively has a context window of 3276 tokens. To increase the context size per request, the total context size must be increased, which naturally has significant impact on memory use. This is most acute on GPU which has a limited available memory.

Memory restrictions thus drive the settings of these two parameters. For reference, a 16Gb GPU can hold a 7B 8-bit model with a context size of 4096 for 10 parallel requests by setting the context size to 40960. If a larger context window is required, the number of parallel requests must be decreased. Likewise, the number of parallel requests can be increased by decreasing the context size. This depends on the requirements of your application.

Inference parameters

Please refer to the general discussion in LLM parameters for setting inference parameters.

Local LLM inference has the following inference parameters that can be sent along with the query:

npredict: the number of tokens to generate. Overrides the maxTokens setting in the model configuration.
temperature: the temperature setting of the model, typically between 0.0 and 1.0.
repeatpenalty: the penalty for repeating tokens.
topk and topp: the probability of token sampling. Lower values tend to produce more coherent and focused text, while higher values introduce more diversity and creativity but potentially more errors or incoherence.

The most significant here are npredict which will stop the token generation process after a certain number of tokens has been generated. Some models can for certain prompts enter a loop where an infinite number of tokens are generated. This is clearly not beneficial situation, so this number should be set to a high enough value so all tokens for a response can be generated, but low enough to stop the model from generating tokens infinitely.

Using GPUs

Using a GPU can significantly speed up token generation and is generally recommended. The discussion above about memory requirements are especially acute when running on GPUs due to memory limitations. In Vespa, the default is to offload the entire model to the GPU if it is available, but by using the gpuLayers parameter one can experiment with offloading parts of the model to GPU.

<services version="1.0">
  <container id="default" version="1.0">

    <!-- Sets up the inference on a mistral 7B model -->
    <component id="local" class="ai.vespa.llm.clients.LocalLLM">
      <config name="ai.vespa.llm.clients.llm-local-client">
          <model url="url/to/mistral-7B-8bit" />
          <parallelRequests>10</parallelRequests>
          <contextSize>40960</contextSize>
          <useGpu>true</useGpu> <!-- default is true -->
          <gpuLayers>100</gpuLayers>
      </config>
    </component>

  </container>
</services>

Here, the model itself has 33 layers, and all are offloaded to the GPU. If your model is too large to fit on the GPU, you can speed up model evaluation by offloading parts of the model to the GPU.

To set up GPUs on self-hosted, please refer to Container GPU setup for more details.

It is very easy to use GPU acceleration on Vespa Cloud. To enable GPU inference, you need to request GPUs on the container nodes. For a more practical introduction, please take a look at the RAG sample app which also demonstrates how to evaluate the LLM on GPUs on Vespa Cloud.