DotNetty发送请求的最佳实践
egmkang 人气:0长链接发送request/response时, 绝大部分包都是小包, 而每个小包都要消耗一个IP包, 成本大约是20-30us, 普通千兆网卡的pps大约是60Wpps, 所以想要提高长链接密集IO的应用性能, 需要做包的合并, 也称为了scatter/gather io或者vector io.
在linux下有readv/writev就是对应这个需求的, 减少系统调用, 减少pps, 提高网卡的吞吐量. 关于readv提高读的速度, 可以看看陈硕muduo里面对于readv的使用, 思路是就是在栈上面弄一个64KB的数组, 组成readv的第二块buffer, 从而尽可能一次性把socket缓冲区的内容全部出来(参见5). 这里不再赘述, 重点描述DotNetty下面怎么做Gathering Write.
首先得有一个Channel<IMessage>, 用来做写的缓冲, 让业务关心业务, 网络关心网络, 否则每个业务都WriteAndFlushAsync, 那是不太可能有合并发送的.
然后就是SendingLoop的主循环, 里面不停的从Channel里面TryRead包, 然后WriteAsync, 隔几个包Flush一次. 类似的思想在Orleans Network里面也存在.
1 public void RunSendLoopAsync(IChannel channel)
2 {
3 var allocator = channel.Allocator;
4 var reader = this.queue.Reader;
5 Task.Run(async () =>
6 {
7 while (!this.stop)
8 {
9 var more = await reader.WaitToReadAsync();
10 if (!more)
11 {
12 break;
13 }
14
15 IOutboundMessage message = default;
16 var number = 0;
17 try
18 {
19 while (number < 4 && reader.TryRead(out message))
20 {
21 Interlocked.Decrement(ref this.queueCount);
22 var msg = message.Inner as IMessage;
23 var buffer = msg.ToByteBuffer(allocator);
24 await channel.WriteAsync(buffer);
25 number++;
26 }
27 channel.Flush();
28 number = 0;
29 }
30 catch (Exception e) when(message != default)
31 {
32 logger.LogError("SendOutboundMessage Fail, SessionID:{0}, Exception:{1}",
33 this.sessionID, e.Message);
34 this.messageCenter.OnMessageFail(message);
35 }
36 }
37 this.logger.LogInformation("SessionID:{0}, SendingLoop Exit", this.sessionID);
38 });
39 }
第19-27行是关键, 这边每4个包做一下flush, 然后flush会触发DotNetty的DoWrite:
1 protected override void DoWrite(ChannelOutboundBuffer input)
2 {
3 List<ArraySegment<byte>> sharedBufferList = null;
4 try
5 {
6 while (true)
7 {
8 int size = input.Size;
9 if (size == 0)
10 {
11 // All written
12 break;
13 }
14 long writtenBytes = 0;
15 bool done = false;
16
17 // Ensure the pending writes are made of ByteBufs only.
18 int maxBytesPerGatheringWrite = ((TcpSocketChannelConfig)this.config).GetMaxBytesPerGatheringWrite();
19 sharedBufferList = input.GetSharedBufferList(1024, maxBytesPerGatheringWrite);
20 int nioBufferCnt = sharedBufferList.Count;
21 long expectedWrittenBytes = input.NioBufferSize;
22 Socket socket = this.Socket;
23
24 List<ArraySegment<byte>> bufferList = sharedBufferList;
25 // Always us nioBuffers() to workaround data-corruption.
26 // See https://github.com/netty/netty/issues/2761
27 switch (nioBufferCnt)
28 {
29 case 0:
30 // We have something else beside ByteBuffers to write so fallback to normal writes.
31 base.DoWrite(input);
32 return;
33 default:
34 for (int i = this.Configuration.WriteSpinCount - 1; i >= 0; i--)
35 {
36 long localWrittenBytes = socket.Send(bufferList, SocketFlags.None, out SocketError errorCode);
37 if (errorCode != SocketError.Success && errorCode != SocketError.WouldBlock)
38 {
39 throw new SocketException((int)errorCode);
40 }
DotNetty TcpSocketChannel类的DoWrite函数, 19行获取当前ChannelOutboundBuffer的Segment<byte>数组, 然后在36行调用Socket.Send一次性发出去, 这个是Gathering Write的关键. 有了这个, 就可以不在业务层用CompositeByteBuffer.
实际上Orleans 3.x做的网络优化, 也有类似的思想:
1 private async Task ProcessOutgoing()
2 {
3 await Task.Yield();
4
5 Exception error = default;
6 PipeWriter output = default;
7 var serializer = this.serviceProvider.GetRequiredService<IMessageSerializer>();
8 try
9 {
10 output = this.Context.Transport.Output;
11 var reader = this.outgoingMessages.Reader;
12 if (this.Log.IsEnabled(LogLevel.Information))
13 {
14 this.Log.LogInformation(
15 "Starting to process messages from local endpoint {Local} to remote endpoint {Remote}",
16 this.LocalEndPoint,
17 this.RemoteEndPoint);
18 }
19
20 while (true)
21 {
22 var more = await reader.WaitToReadAsync();
23 if (!more)
24 {
25 break;
26 }
27
28 Message message = default;
29 try
30 {
31 while (inflight.Count < inflight.Capacity && reader.TryRead(out message) && this.PrepareMessageForSend(message))
32 {
33 inflight.Add(message);
34 var (headerLength, bodyLength) = serializer.Write(ref output, message);
35 MessagingStatisticsGroup.OnMessageSend(this.MessageSentCounter, message, headerLength + bodyLength, headerLength, this.ConnectionDirection);
36 }
37 }
38 catch (Exception exception) when (message != default)
39 {
40 this.OnMessageSerializationFailure(message, exception);
41 }
42
43 var flushResult = await output.FlushAsync();
44 if (flushResult.IsCompleted || flushResult.IsCanceled)
45 {
46 break;
47 }
48
49 inflight.Clear();
50 }
核心在31行, 开始写, 43行开始flush, 只不过Orleans用的pipelines io, DotNetty是传统模型.
这样做, 可以在有限的pps下, 支撑更高的吞吐量.
个人感觉DotNetty更好用一些.
参考:
1. https://github.com/Azure/DotNetty/blobhttps://img.qb5200.com/download-x/dev/src/DotNetty.Transport/Channels/Sockets/TcpSocketChannel.cs#L271-L288
2. https://github.comhttps://img.qb5200.com/download-x/dotnet/orleans/blob/master/src/Orleans.Core/Networking/Connection.cs#L282-L294
3. https:/https://img.qb5200.com/download-x/docs.microsoft.com/zh-cn/windows/win32/winsock/scatter-gather-i-o-2
4. https://linux.die.net/man/2/writev
5. https://github.com/chenshuo/muduo/blobhttps://img.qb5200.com/download-x/d980315dc054b122612f423ee2e1316cb14bd3b5/muduo/net/Buffer.cc#L28-38
加载全部内容