why grpc-java uds is slower than dns?

Question

Question:

We did a test to compare the performance between uds and dns. According to what said on the Internet, uds should be faster because it lacks many network layer protocols. However, the actual tested found that uds is at most the same as dns,in most cases The performance will be worse. Can anyone help explain ? The following are test cases and test results.

ENV:
jdk: jdk-17.0.10
grpc: 1.61.1
test machine: centos 7.9 & 64 cpu cores & 251 GB RAM

code detail

uds server core code:

 String UDS_FILE="/tmp/grpc_uds.socket";
 server = NettyServerBuilder.forAddress(new DomainSocketAddress(UDS_FILE))
                    .bossEventLoopGroup(new EpollEventLoopGroup())
                    .workerEventLoopGroup(new EpollEventLoopGroup())
                    .channelType(EpollServerDomainSocketChannel.class)
                    .maxInboundMessageSize(4*1024*1024)
                    .addService(BrSpringApplication.getBean(GreeterServiceImple.class))
                    .build().start();
  blockUtilShutDown();

uds client core code:

 String socketPath="/tmp/grpc_uds.socket";
 channel = NettyChannelBuilder.forAddress(new DomainSocketAddress(socketPath))
                    .eventLoopGroup(new EpollEventLoopGroup())
                    .channelType(EpollDomainSocketChannel.class)
                    .maxInboundMessageSize(4 * 1024 * 1024)
                    .usePlaintext().build();
GreeterGrpc.GreeterBlockingStub blockStub = GreeterGrpc.newBlockingStub(channel);
HelloRequest request = HelloRequest.newBuilder().setName(paramJson.toJSONString()).build();
        HelloReply response = getBlockStub().sayHello(request);

GreeterServiceImpl.java

@Override
    public void sayHello(HelloRequest request, StreamObserver<HelloReply> responseObserver) {
        long startTime = System.currentTimeMillis();
        logger.warn("request:{}", request.getName());
        try {
            if (Context.current().isCancelled()) {
                logger.warn("deadline cancalled,deadline:{}", Context.current().getDeadline());
                responseObserver.onError(new Exception("Cancelled by client"));
                return;
            }
            JSONObject msgRequest= JSONObject.parseObject(request.getName());
            int num=msgRequest.getIntValue("factor");
            String msg=msgRequest.getString("message");
            StringBuilder messageBack = new StringBuilder("rep-");
            for (int i = 0; i < num; i++) {
                messageBack.append(msg).append("|");
            }
//            logger.warn("response:{}", messageBack);
            HelloReply response = HelloReply.newBuilder().setMessage(messageBack + ",ms:" + (System.currentTimeMillis() - startTime)).build();
            responseObserver.onNext(response);
            responseObserver.onCompleted();

        } catch (BrException e) {
            logger.error("BrException,code:{},message:{}", e.getCode(), e.getMessage());
            HelloReply response = HelloReply.newBuilder().setMessage(e.getMessage()).build();
            responseObserver.onNext(response);
            responseObserver.onCompleted();
        } catch (Exception ex) {
            logger.error("sys error", ex);
            HelloReply response=HelloReply.newBuilder().setMessage(ex.getMessage()).build();
            responseObserver.onNext(response);
            responseObserver.onCompleted();
        }
    }

dns sever core code:

String port="80";
server = NettyServerBuilder.forPort(port)
                    .maxInboundMessageSize(4*1024*1024)
                    .addService(BrSpringApplication.getBean(GreeterServiceImple.class))
                    .build().start();
blockUtilShutDown();

dns client core code:

String ip="localhost:80"
channel = ManagedChannelBuilder.forTarget(ip).usePlaintext().build();
GreeterGrpc.GreeterBlockingStub blockStub = GreeterGrpc.newBlockingStub(channel);
HelloRequest request = HelloRequest.newBuilder().setName(paramJson.toJSONString()).build();
        HelloReply response=getBlockStub().sayHello(request);

test result:

client message size	response message size	thead	totalnum	type	num	total cost(ms)	qps
12B	60B	50	5000000	dns	1	127359ms	5535.790199357721
12B	60B	50	5000000	dns	2	126051ms	5593.233722858208
12B	60B	50	5000000	dns	3	128828ms	5472.666687366101
12B	60B	50	5000000	uds	1	133212ms	5292.561510974987
12B	60B	50	5000000	uds	2	128315ms	5494.546265050852
12B	60B	50	5000000	uds	3	127177ms	5543.712337922738
12B	120B	50	5000000	dns	1	125919ms	5599.097070338868
12B	120B	50	5000000	dns	2	122034ms	5777.346509989019
12B	120B	50	5000000	dns	3	120439ms	5853.857172510566
12B	120B	50	5000000	uds	1	123538ms	5707.010830675582
12B	120B	50	5000000	uds	2	126988ms	5551.963209122122
12B	120B	50	5000000	uds	3	126450ms	5575.584847765916
12B	6kb	50	5000000	dns	1	123176ms	5723.783074624926
12B	6kb	50	5000000	dns	2	127242ms	5540.880401125414
12B	6kb	50	5000000	dns	3	121556ms	5800.06502352825
12B	6kb	50	5000000	uds	1	131939ms	5343.626251525327
12B	6kb	50	5000000	uds	2	133399ms	5285.1423473939085
12B	6kb	50	5000000	uds	3	130091ms	5419.534817935138
5kb	5kb	50	5000000	dns	1	133404ms	5284.9442595424425
5kb	5kb	50	5000000	dns	2	130532ms	5401.225017620201
5kb	5kb	50	5000000	dns	3	130145ms	5417.286134695916
5kb	5kb	50	5000000	uds	1	140809ms	5007.0144948121215
5kb	5kb	50	5000000	uds	2	140685ms	5011.427685965099
5kb	5kb	50	5000000	uds	3	140992ms	5000.515660463005

I expected grpc uds to be faster than dns , but it's not. all test cases are on the localhost machine , and i put the uds path to the ssd disk , but fount it's performance as same as hdd. I alse changed server and client memory from 2GB to 6 GB ,but it doesn't any improvement