Multi-Core Speedup

All performance tests are executed with single physical core and with multiple cores scenarios.

Intel Hyper-Threading (HT)

Intel Xeon processors used in CSIT can operate either in HT Disabled mode (single logical core per each physical core) or in HT Enabled mode (two logical cores per each physical core). HT setting is applied in BIOS and requires server SUT reload for it to take effect, making it impractical for continuous changes of HT mode of operation.

CSIT-2110 performance tests are executed with server SUTs’ Intel XEON processors configured with Intel Hyper-Threading Enabled for all Xeon Skylake and Xeon Cascadelake testbeds.

More information about physical testbeds is provided in Performance Physical Testbeds.

Multi-core Tests

CSIT-2110 multi-core tests are executed in the following VPP worker thread and physical core configurations:

  1. Intel Xeon Skylake and Cascadelake testbeds (2n-skx, 3n-skx, 2n-clx) with Intel HT enabled (2 logical CPU cores per each physical core):

  1. 2t1c - 2 VPP worker threads on 1 physical core.

  2. 4t2c - 4 VPP worker threads on 2 physical cores.

  3. 8t4c - 8 VPP worker threads on 4 physical cores.

VPP worker threads are the data plane threads running on isolated logical cores. With Intel HT enabled VPP workers are placed as sibling threads on each used physical core. VPP control threads (main, stats) are running on a separate non-isolated core together with other Linux processes.

In all CSIT tests care is taken to ensure that each VPP worker handles the same amount of received packet load and does the same amount of packet processing work. This is achieved by evenly distributing per interface type (e.g. physical, virtual) receive queues over VPP workers using default VPP round-robin mapping and by loading these queues with the same amount of packet flows.

If number of VPP workers is higher than number of physical or virtual interfaces, multiple receive queues are configured on each interface. NIC Receive Side Scaling (RSS) for physical interfaces and multi-queue for virtual interfaces are used for this purpose.

Section Speedup Multi-Core includes a set of graphs illustrating packet throughout speedup when running VPP worker threads on multiple cores. Note that in quite a few test cases running VPP workers on 2 or 4 physical cores hits the I/O bandwidth or packets-per-second limit of tested NIC.