SPRACT8 September   2020 66AK2H06 , 66AK2H12 , 66AK2H14

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 TI Processor SDK RTOS
    2. 1.2 TI NDK
    3. 1.3 66AK2H Device
    4. 1.4 FTP Offering in TI Processor SDK RTOS
  4. 2Hardware and Software
  5. 3Develop the FTP Server on K2H
    1. 3.1 Reference FTP Server Example
    2. 3.2 Create K2H FTP Server Example
    3. 3.3 Test K2H FTP Server Example
  6. 4Performance Tuning
    1. 4.1 Quick Code Check
      1. 4.1.1 FTP Transmitting Code Check
      2. 4.1.2 FTP Receiving Code Check
      3. 4.1.3 CCS Project Optimization
    2. 4.2 Increase the TCP Buffer Sizes
    3. 4.3 UIA CPU Load Instrumentation
    4. 4.4 What Can We Do on the PC Side?
      1. 4.4.1 TCP Window Scaling Check
      2. 4.4.2 Receive Interrupt Coalescing Check
    5. 4.5 What Else Can We Do on the K2H Side?
      1. 4.5.1 TCP/IP Checksum Offloading Check
      2. 4.5.2 NIMU Driver Efficiency Profiling
      3. 4.5.3 Receive Interrupt Coalescing
    6. 4.6 Final FTP Throughput Results
  7. 5Summary
  8. 6References

4.4.2 Receive Interrupt Coalescing Check

As shown from the packet capture, the data transfer size is 1514 bytes from the K2H EVM to the PC. The PC sends an ACK packet for every 2920 bytes (2 packets) received by examining the successive ACK packets’ acknowledge number field:

GUID-20200819-CA0I-3PZQ-2H7N-DK5RX18R73RP-low.png Figure 4-9 Wireshark Analysis of ACK Packet Frequency

The frequent reception of TCP ACK packets drives up the CPU usage during receiving interrupt handling. The way to reduce the interrupt generation and hence the interrupt handling is called interrupt coalescing. It prevents interrupts from being raised to a CPU until a specific amount of events are pending. The CPU is relaxed and the throughput can be potentially increased with fewer interrupts.

Interrupt coalescing can be explored on either side, or both sides. From the Windows 10 PC side, if the generated TCP ACK packets can be suppressed to less frequent, then the K2H CPU saves the power for receiving interrupt handling. The interrupt coalescing is configured in the Windows 10 registry under Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\\{Interface_name}, one can use regedit utility to add two additional fields: TcpAckFrequency and TcpDelAckTicks. An ACK packet is transmitted every receiving number of TcpAckFrequency packets or when TcpDelAckTicks (in unit of 100 millisecond) delay timer expires, whichever happens first. An example is depicted below:

GUID-20200819-CA0I-5XHM-BJCH-GKSK4G68TSHP-low.png Figure 4-10 Windows PC Interrupt Coalescing Configuration

Those numbers are based on trials and the PC needs to reboot for the setting to take into effect. With TcpAckFrequency = 10 and TcpDelAckTicks = 1, the ACK is now transmitted for every 10 (from 2) received packets:

GUID-20200819-CA0I-4NXK-MFDC-3FQ8LBKB9D1B-low.png Figure 4-11 Effect of Interrupt Coalescing Setting on ACK Packet Generation