ARFS Policy for CPU Cache Hit Rate in Cisco UCS

300-610 By islever Editorial Last updated

Describe compute requirements for AI/ML applications

Short answer

B Accelerated Receive Flow Steering (ARFS) increases the CPU data cache hit rate by steering packet processing to the application thread's CPU core.

Question

A network consultant evaluates the Ethernet Adapter Policy configuration to be applied to the Cisco UCS blade servers. The policy must minimize latency and increase throughput for sensitive applications. The solution must increase the CPU data cache hit rate to meet these requirements. Which policy is required?
  1. RDMA
  2. ARFS Correct Answer
  3. AIC
  4. NVM-e

Key Takeaways

The question tests knowledge of network adapter features that optimize CPU performance, specifically identifying ARFS as the mechanism for improving cache locality.

Accelerated Receive Flow Steering (ARFS) is the required policy to minimize latency and increase throughput by maximizing CPU data cache hit rates in Cisco UCS blade servers.

Common mistake: Candidates often select RDMA, confusing low-level hardware offloading with software-based CPU scheduling optimizations.

Expert Analysis

Why the Answer Is Correct

The correct answer is B, ARFS. Accelerated Receive Flow Steering (ARFS) is a feature that allows the network adapter to steer incoming packet processing to specific CPU cores where the application thread resides. By keeping the processing on the same core, it significantly increases the CPU data cache hit rate, thereby reducing latency and increasing throughput.

Why the Other Options Are Wrong

RDMA (Remote Direct Memory Access) offloads data movement from the CPU entirely, which does not directly address the requirement to improve the CPU's own data cache hit rate through steering. AIC (Accelerated I/O Virtualization) focuses on virtualization efficiency rather than single-threaded cache locality. NVM-e is a storage protocol standard and is not an Ethernet adapter policy for receive flow steering.

Community Comment Notes

The community consensus strongly supports ARFS, with one user noting that it "steer[s] kernel level processing... to the CPU where the application thread consuming the packet is running." While some users initially considered RDMA due to its performance benefits, the specific mention of "CPU data cache hit rate" points definitively to ARFS.

Official Reference

https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/ucs-manager/GUI-User-Guides/Network-Mgmt/3-2/b_UCSM_Network_Mgmt_Guide_3_2/b_UCSM_Network_Mgmt_Guide_3_2_chapter_01001.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When questions mention 'cache hit rate' or 'application thread affinity' in the context of NIC policies, look for ARFS or RSS variants rather than pure offloading technologies like RDMA.

Frequently Asked Questions

Why is RDMA incorrect for this scenario?

RDMA bypasses the CPU stack entirely, whereas the question specifically asks for improvements to the CPU's own data cache hit rate via steering.

How does ARFS differ from standard RSS?

ARFS provides hardware-assisted steering that updates the kernel's flow table dynamically, ensuring packets are processed on the core where the socket is open, improving cache locality.

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Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. k3rnelpanicpj 👍 1 Answered B
    Accelerated Receive Flow Steering (ARFS) is hardware-assisted receive flow steering that can increase CPU data cache hit rate by steering kernel level processing of packets to the CPU where the application thread consuming the packet is running.
  2. b44c199 👍 1
    https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/ucs-manager/GUI-User-Guides/Network-Mgmt/3-2/b_UCSM_Network_Mgmt_Guide_3_2/b_UCSM_Network_Mgmt_Guide_3_2_chapter_01001.html
  3. lurker8000 👍 1
    I think it's RDMA, A
  4. Wasamela 👍 1
    Correct

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