Russell BryantandGitHub
e489ad7a21
- **Add SPDX license headers to python source files** - **Check for SPDX headers using pre-commit** commit 9d7ef44c3cfb72ca4c32e1c677d99259d10d4745 Author: Russell Bryant <rbryant@redhat.com> Date: Fri Jan 31 14:18:24 2025 -0500 Add SPDX license headers to python source files This commit adds SPDX license headers to python source files as recommended to the project by the Linux Foundation. These headers provide a concise way that is both human and machine readable for communicating license information for each source file. It helps avoid any ambiguity about the license of the code and can also be easily used by tools to help manage license compliance. The Linux Foundation runs license scans against the codebase to help ensure we are in compliance with the licenses of the code we use, including dependencies. Having these headers in place helps that tool do its job. More information can be found on the SPDX site: - https://spdx.dev/learn/handling-license-info/ Signed-off-by: Russell Bryant <rbryant@redhat.com> commit 5a1cf1cb3b80759131c73f6a9dddebccac039dea Author: Russell Bryant <rbryant@redhat.com> Date: Fri Jan 31 14:36:32 2025 -0500 Check for SPDX headers using pre-commit Signed-off-by: Russell Bryant <rbryant@redhat.com> --------- Signed-off-by: Russell Bryant <rbryant@redhat.com>
Distributed KV cache transfer
This folder implements distributed KV cache transfer across vLLM instances. Currently the main usecase is for disaggregated prefilling.
Abstractions
The KV cache transfer contains three layer of abstractions:
- KV pipe: a FIFO pipe for torch.tensor transmission. Key APIs:
send_tensorandrecv_tensor. - KV lookup buffer: a lookup buffer for KV caches. Key: the tokens, value: the KV caches (and/or hidden states). Key APIs:
insertanddrop_select(similar to SQL semantics). - KV connector: a connector that connects the KV pipe and KV lookup buffer to vLLM. Key APIs:
send_kv_caches_and_hidden_statesandrecv_kv_caches_and_hidden_states.
Why we need KV lookup buffer: FIFO pipe itself is not enough as prefill vLLM worker may process requests in a different order compared to decode vLLM worker. Say the QPS is really high, prefill worker may handle requests in order A -> B -> C, but the decode worker may process request C first. This is not the case that can be naturally handled by FIFO pipe, so we provide KV lookup buffer to help translate a FIFO pipe to a lookup buffer.
NOTE: KV pipe layer is bypassible: you can skip this layer if your distributed communication service already supports key-value-based lookup (like redis or RDMA database).
NOTE: If you want to not only transfer KV caches, but adjust the model execution flow of vLLM as well (for example, allow vLLM to receive KV caches on some tokens and do prefill on the remaining tokens), you can bypass both KV pipe layer and KV lookup buffer layer, and directly implement on KV connector layer. Bear in mind that as vLLM's model input is constantly changing, this implementation will likely be broken when vLLM has new updates.
Disaggregated prefilling
The example usage is in this file.
Here is the diagram of how we run disaggretgated prefilling.
