如果Akka-Http WebSocket处理传入消息非常缓慢，你可以尝试以下解决方法：

1. 使用合适的线程池：默认情况下，Akka-Http使用的是一个全局的线程池，这可能会导致处理消息的阻塞。你可以使用自定义的线程池来处理WebSocket连接的消息。例如，你可以创建一个专门用于WebSocket处理的线程池，并将其配置为适当的大小。

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model.ws.{Message, TextMessage}
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import akka.stream.scaladsl.{Flow, Sink, Source}

import scala.concurrent.ExecutionContext

object WebSocketServer {
  def main(args: Array[String]): Unit = {
    implicit val system: ActorSystem = ActorSystem("WebSocketServer")
    implicit val materializer: ActorMaterializer = ActorMaterializer()
    implicit val ec: ExecutionContext = system.dispatcher

    val websocketFlow: Flow[Message, Message, Any] = Flow[Message].mapConcat {
      case TextMessage.Strict(text) =>
        // Process the incoming message here
        // Return a list of outgoing messages
        // e.g. List(TextMessage("Response"))
        List(TextMessage("Response"))
      case _ =>
        List.empty
    }

    val route = path("ws") {
      get {
        handleWebSocketMessages(websocketFlow)
      }
    }

    Http().bindAndHandle(route, "localhost", 8080)
  }
}

2. 调整缓冲区大小：通过调整缓冲区大小，你可以增加消息的处理能力。可以使用buffer操作符来设置缓冲区的大小。

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model.ws.{Message, TextMessage}
import akka.http.scaladsl.server.Directives._
import akka.stream.{ActorMaterializer, OverflowStrategy}
import akka.stream.scaladsl.{Flow, Sink, Source}

import scala.concurrent.ExecutionContext

object WebSocketServer {
  def main(args: Array[String]): Unit = {
    implicit val system: ActorSystem = ActorSystem("WebSocketServer")
    implicit val materializer: ActorMaterializer = ActorMaterializer()
    implicit val ec: ExecutionContext = system.dispatcher

    val websocketFlow: Flow[Message, Message, Any] =
      Flow[Message]
        .buffer(10, OverflowStrategy.dropNew)
        .mapConcat {
          case TextMessage.Strict(text) =>
            // Process the incoming message here
            // Return a list of outgoing messages
            // e.g. List(TextMessage("Response"))
            List(TextMessage("Response"))
          case _ =>
            List.empty
        }

    val route = path("ws") {
      get {
        handleWebSocketMessages(websocketFlow)
      }
    }

    Http().bindAndHandle(route, "localhost", 8080)
  }
}

通过采取上述措施，你应该能够提高Akka-Http WebSocket处理传入消息的性能和响应速度。