25 GbE and 100GbE ethernet devices not reaching expected performance on a system with an AMD EPYC CPU.

Solution In Progress - Updated -

Environment

  • Red Hat Enterprise Linux 7.4
  • AMD EPYC based servers
  • 25Gb or 100Gb Ethernet adapter

Issue

  • Getting lower than expected performance from 25GbE and 100GbE adapters on AMD EPYC based systems.
  • AMD Naples IOMMU interference with networking processing

Resolution

A fix for this issue is planned for release in a future version of Red Hat Enterprise Linux 7.

Until then the suggested workaround is to boot the system with the kernel argument "iommu=pt". More information on how to make this change persistent is available here.

Root Cause

With newer, higher speed devices, perf data shows that the amount of MMIO that is performed when submitting commands to the IOMMU causes performance issues.

A fix for the issue has been accepted upstream and is planned for inclusion in a future update to Red Hat Enterprise Linux 7.

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.

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