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Increasing the Number of Samples

Last Modified: May 14, 2020

Increase the number of samples to achieve greater throughput in Ethernet- and PCIe-based streaming.

Complete the following procedure to improve data streaming performance:

  1. Increase the number of samples using one of the following options:
    • Increase the number of samples given for niUSRP Write TX Data or niUSRP Fetch RX Data. This will result in greater throughput during streaming.
    • Increase the number of samples to an exact multiple of the maximum Ethernet or PCIe packet size. This will also result in greater throughput because smaller packets are not required to transfer all the data.
  2. Change the maximum throughput for your streaming method using one of the following options:
    • For PCIe-based streaming, use samples in multiples of 1,020 per call for a 16-bit sample width to ensure that all PCIe packets are of optimal size for maximum throughput.
    • For Ethernet-based streaming, use the following equation to calculate the number of samples that results in the maximum throughput:
      Write Size Multiple To Maximize Throughput = ( UDP Payload Size CVITA Headers ) Bytes Per Sample

      where

      • CVITA headers = 16 bytes
      • bytes per sample = 4 bytes per sample for I and Q components.

    Use the optimal write size multiple for maximum throughput in various configurations.

    Table 1. Optimal Write Size Multiple
    MTU Size UDP Payload Size Samples Per Packet (8-bit Samples) Samples Per Packet (16-bit Samples)
    1,500 1,472 728 364
    8,000 7,972 3,978 1,989
    9,000 8,000 3,992 1,996

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