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Thread Affinity

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If you're developing low-latency network applications with Netty, you're probably aware of the thing called thread affinity. Thread affinity can be used to force your application threads to run on a particular CPU core or set of CPUs. By doing so, you can eliminate threads migration during the operating system scheduling process. Fortunately, there's a java library called Java-Thread-Affinity which can be easily integrated with your Netty application.

First, add the following dependency to your Maven pom.xml file:

<dependency>
    <groupId>net.openhft</groupId>
    <artifactId>affinity</artifactId>
    <version>3.0.6</version>
</dependency>

Second, create an AffinityThreadFactory with a particular strategy and pass it to the EventLoopGroup which would contain latency-sensitive threads. Here's an example:

final int acceptorThreads = 1;
final int workerThreads = 10;
EventLoopGroup acceptorGroup = new NioEventLoopGroup(acceptorThreads);
ThreadFactory threadFactory = new AffinityThreadFactory("atf_wrk", AffinityStrategies.DIFFERENT_CORE);
EventLoopGroup workerGroup = new NioEventLoopGroup(workerThreads, threadFactory);

ServerBootstrap serverBootstrap = new ServerBootstrap().group(acceptorGroup, workerGroup);

Notice, to achieve the lowest latency possible you should consider isolating your target CPUs from OS scheduler. Isolating target CPUs will prevent OS scheduler to schedule any other user-space processes on these CPUs. This can be done with isolcpus kernel boot parameter (i.e. add isolcpus=<cpu-list> to grub.conf).

For more information, please visit the project's Github.

Last retrieved on 25-Sep-2017