Tune kernel parameters

You can further optimize network performance by adjusting Linux kernel parameters and testing across different environments, including local-to-cloud scenarios.

Connect from a local machine

You can look at ways to mitigate performance degradation due to events such as packet loss.

In this example, you will connect to the server node a local machine to demonstrate a longer response time. Check the iPerf3 installation guide to install iPerf3 on other operating systems.

Before starting the test:

• Update your cloud server’s security group to allow incoming TCP connections from your local machine’s public IP.
• Use the public IP address of the cloud instance when connecting.

Running iPerf3 on the local machine and connecting to the cloud server shows a longer round trip time, in this example more than 40ms.

Run this command on your local computer:

    

        
        
iperf3 -c <server-public-IP> -v

    

Compared to over 2 Gbit/sec within AWS, this test shows a reduced bitrate (~157 Mbit/sec) due to longer round-trip times (for example, >40ms).

    

        
        Starting Test: protocol: TCP, 1 streams, 131072 byte blocks, omitting 0 seconds, 10 second test, tos 0
...
Test Complete. Summary Results:
[ ID] Interval           Transfer     Bitrate
[  8]   0.00-10.01  sec   187 MBytes   157 Mbits/sec                  sender
[  8]   0.00-10.03  sec   187 MBytes   156 Mbits/sec                  receiver

        
    

Modify kernel parameters on the server

On the server, you can configure Linux kernel runtime parameters with the sysctl command.

There are a plethora of values to tune that relate to performance and security. The following command can be used to list all available options. The Linux kernel documentation provides a more detailed description of each parameter.

    

        
        
sysctl -a | grep tcp

    

    

        
        
net.ipv4.tcp_available_congestion_control = reno cubic

    

Increase TCP buffer sizes

You can increase the kernel’s read and write buffer sizes on the server improve throughput on high-latency connections. This consumes more system memory but allows more in-flight data.

To try it, run the following commands on the server:

    

        
        
sudo sysctl net.core.rmem_max=134217728 # default = 212992
sudo sysctl net.core.wmem_max=134217728 # default = 212992

    

Then, restart the iPerf3 server:

    

        
        
iperf3 -s

    

Now rerun iPerf3 again on your local machine:

    

        
        
iperf3 -c <server-public-IP> -v

    

Without changing anything on the client, the throughput improved by over 60%.

    

        
        Test Complete. Summary Results:
[ ID] Interval           Transfer     Bitrate
[  8]   0.00-10.00  sec   308 MBytes   258 Mbits/sec                  sender
[  8]   0.00-10.03  sec   307 MBytes   257 Mbits/sec                  receiver

        
    

You’ve now completed a guided introduction to:

• Network performance microbenchmarking
• Simulating real-world network conditions
• Tuning kernel parameters for high-latency links

You can now explore this area further by testing other parameters, tuning for specific congestion control algorithms, or integrating these benchmarks into CI pipelines for continuous performance evaluation.