Oversubscription of hardware resources in AMD Instinct accelerators#
2024-10-11
4 min read time
When an AMD Instinct™ MI series accelerator enters an oversubscribed state, the amdgpu driver outputs the following
message.
amdgpu: Runlist is getting oversubscribed. Expect reduced ROCm performance.
Oversubscription occurs when application demands exceed the available hardware resources. In an oversubscribed state, the hardware scheduler tries to manage resource usage in a round-robin fashion. However, this can result in reduced performance, as resources might be occupied by applications or queues not actively submitting work. The granularity of hardware resources occupied by an inactive queue can be in the order of milliseconds, during which the accelerator or GPU is effectively blocked and unable to process work submitted by other queues.
What triggers oversubscription?#
The system enters an oversubscribed state when one of the following conditions is met:
Hardware queue limit exceeded: The number of user-mode compute queues requested by applications exceeds the hardware limit of 24 queues for current Instinct accelerators.
Virtual memory context slots exceeded: The number of user processes exceeds the number of available virtual memory context slots, which is 11 for current Instinct accelerators.
Multiple processes using cooperative workgroups: More than one process attempts to use the cooperative workgroup feature, leading to resource contention.