thread configuration (names & QoS on Darwin) #2943
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Lukasa
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### Motivation: On Darwin, QoS (quality of service) of threads plays an important role, especially on Apple Silicon machines with P-cores and E-cores. If you spawn raw threads (like NIOPosix) and use a mechanism that doesn't support QoS propagation (like reading/writing to networks -- like NIOPosix does), it's recommended to default to the main thread's QoS. Otherwise you'll always be at the default QoS for "legacy" threads which means bad latencies, especially on Apple Silicon machines. In a follow-up PR #2943 we're adding better configurability for thread configuration. ### Modifications: Default to main thread QoS on Darwin. ### Result: Better latencies for applications with higher QoS classes.
glbrntt
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Nov 6, 2024
| @@ -70,7 +70,7 @@ public final class MultiThreadedEventLoopGroup: EventLoopGroup { | |||
| private let index = ManagedAtomic<Int>(0) | |||
| private var eventLoops: [SelectableEventLoop] | |||
| private let shutdownLock: NIOLock = NIOLock() | |||
| private let threadNamePrefix: String | |||
| private let threadNamePrefix: String? | |||
| @@ -108,7 +108,8 @@ public final class MultiThreadedEventLoopGroup: EventLoopGroup { | |||
| } | |||
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| private static func setupThreadAndEventLoop( | |||
| name: String, | |||
| name: String?, | |||
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How come name is optional now?
| #endif | ||
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| public struct NIOThreadConfiguration: Sendable { | ||
| public var threadNamePrefix: Optional<String> |
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Can you document how this is used and the recommendations for its value? I know from looking at some examples that "-" is necessary for the various groupings and also that the prefix should be reasonably short.
Can you document what nil means in this context too?
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Motivation:
For the longest time, NIO only had internal APIs to choose the thread names and on Darwin, there was no way to assign the NIO threads certain QoS classes. That meant that on Darwin (e.g. macOS) you would always get poor latencies with NIOPosix, particularly on Apple Silicon machines where NIO might sometimes be restricted to the E-cores.
Modifications:
NIOThreadConfigurationwhich lets you configure a thread name prefix & QoS on DarwinResult: