Avoiding Cross-Datacenter Collective Congestion via Disaggregated Buffering
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arXiv
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| Format: | Preprint |
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2026
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| author | Scazzariello, Mariano Rotman, Noga H. Gavrilenko, Dima Khashab, Sajy Shpiner, Alexander Kadosh, Matty Chiesa, Marco Kostic, Dejan Silberstein, Mark |
| author_facet | Scazzariello, Mariano Rotman, Noga H. Gavrilenko, Dima Khashab, Sajy Shpiner, Alexander Kadosh, Matty Chiesa, Marco Kostic, Dejan Silberstein, Mark |
| contents | LLM training at the scale of tens of thousands of GPUs now spans multiple datacenters (DC), making cross-DC collectives over long-haul links unavoidable. A critical and overlooked bottleneck arises when these collectives collide with intra-DC traffic at the destination - a common pattern in real workloads. The multi-millisecond congestion control loop is too slow to react, triggering severe packet loss and congestion collapse.
We present Spillway, a transparent in-network mechanism that buffers dropped packets in switch-disaggregated buffers in a destination data center and drains them once congestion subsides. Through large-scale end-to-end simulations and a hardware prototype, we show that Spillway eliminates performance degradation from collective collisions, reducing iteration time by up to 14 %, without changes to end hosts or training frameworks. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_11852 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Avoiding Cross-Datacenter Collective Congestion via Disaggregated Buffering Scazzariello, Mariano Rotman, Noga H. Gavrilenko, Dima Khashab, Sajy Shpiner, Alexander Kadosh, Matty Chiesa, Marco Kostic, Dejan Silberstein, Mark Networking and Internet Architecture LLM training at the scale of tens of thousands of GPUs now spans multiple datacenters (DC), making cross-DC collectives over long-haul links unavoidable. A critical and overlooked bottleneck arises when these collectives collide with intra-DC traffic at the destination - a common pattern in real workloads. The multi-millisecond congestion control loop is too slow to react, triggering severe packet loss and congestion collapse. We present Spillway, a transparent in-network mechanism that buffers dropped packets in switch-disaggregated buffers in a destination data center and drains them once congestion subsides. Through large-scale end-to-end simulations and a hardware prototype, we show that Spillway eliminates performance degradation from collective collisions, reducing iteration time by up to 14 %, without changes to end hosts or training frameworks. |
| title | Avoiding Cross-Datacenter Collective Congestion via Disaggregated Buffering |
| topic | Networking and Internet Architecture |
| url | https://arxiv.org/abs/2605.11852 |