Executive summary: Jira ticket VPP-2072 [4] describes how random RSS keys make some performance test results too random to be useful. This vpp-dev thread can be used for discussing ways how to make CSIT results deterministic.
Longer version: As far as I can tell, dpdk plugin + ICE driver is the only combination of VPP plugin and NIC driver (of those currently tested in CSIT) that uses random RSS keys. As the goal of CSIT performance testing is to detect performance changes, we want to avoid any avoidable randomness. Previously, AVF plugin had the same issue, and it was changed [5] to use a static RSS key. Additionally, it was the same key as dpdk plugin with i40e driver uses, which means the performance comparison of the two plugins is now fairer. (The distribution of traffic flows over VPP workers is now the same.) We (CSIT) want to make dpdk plugin use a static RSS key also with ICE driver, but it is not clear how we (VPP) should implement it. Some options: 1. Add a patch file (to build/external/patches/). 2. Leverage a more official DPDK API (if available). 3. Wait for next DPDK version with a better support. If we want to offer users the choice (random, static, or even user provided RSS key), the question is how users would specify it (startup.conf, binary API, …). I imagine other apps (not just VPP dpdk plugin) may also want deterministic RSS, so a long-term solution will be in DPDK code (that is why I added bunch of DPDK people to To and Cc). In the meantime, VPP can apply any medium-term workaround. Note that VPP 22.03 is already released, and the primary CSIT testbed affected (3n-snr) has hyperthreading off, so 1-core tests are not affected. Other testbeds usually do not test with small number of flows or at least offer a different NIC. All that means this issue is not a high priority. Vratko. [4] https://jira.fd.io/browse/VPP-2072 [5] https://gerrit.fd.io/r/c/vpp/+/33705/2/src/plugins/avf/device.c
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