本文深入探讨了Redis6.0中引入的多线程IO特性，以及它如何通过并发处理网络数据的读写和协议解析，来提升Redis的性能。文章详细介绍了多线程IO的配置参数、执行流程，并分析了相关的源代码。通过与Redis6.0的单线程模型对比，揭示了多线程IO在提高访问请求处理能力上的优势。此外，文章还提到了Valkey8.0版本中异步IO的进一步优化，为读者提供了更全面的技术视角。

💡 Redis6.0引入多线程IO，主要用于处理网络数据的读写和协议解析，而命令执行仍保持单线程，默认不开启。通过设置io-threads参数大于1来启用，但不能超过128，且在运行时不可动态修改。

💡 Redis6.0多线程IO的执行流程包括：主线程接收连接，分配socket给IO线程；IO线程读取并解析请求数据；主线程执行命令；主线程将回写事件分配给IO线程；IO线程回写数据。主线程和IO线程分工协作，提高效率。

💡 主线程在beforeSleep函数中，将待读数据客户端分发给IO线程，并等待IO线程完成读操作。IO线程负责从socket读取数据、解析命令，主线程则负责执行命令。这种模式实现了读写分离，提高了并发处理能力。

原创 竹径 2025-06-16 18:30 上海

通过开启多线程 IO，并设置合适的 CPU 数量，可提升访问请求至一倍以上。Redis6.0多线程 IO 仍存在一些不足，未充分利用 CPU 核心，在最新的 Valkey8.0 版本中，引入异步 IO 将进一步大幅提升 Valkey 性能。

# io-threads 4  IO 线程数量
# io-threads-do-reads no  读数据及数据解析是否也用 IO 线程

/* Initialize the data structures needed for threaded I/O. */
void initThreadedIO(void) {
    io_threads_active = 0; /* We start with threads not active. */
    
    /* Don't spawn any thread if the user selected a single thread:
     * we'll handle I/O directly from the main thread. */
    if (server.io_threads_num == 1) return;
    
    if (server.io_threads_num > IO_THREADS_MAX_NUM) {
        serverLog(LL_WARNING,"Fatal: too many I/O threads configured. "
                             "The maximum number is %d.", IO_THREADS_MAX_NUM);
        exit(1);
    }
   
    /* Spawn and initialize the I/O threads. */
    for (int i = 0; i < server.io_threads_num; i++) {
        /* Things we do for all the threads including the main thread. */
        io_threads_list[i] = listCreate();
        if (i == 0) continue; /* Thread 0 is the main thread. */
       
        /* Things we do only for the additional threads. */
        pthread_t tid;
        pthread_mutex_init(&io_threads_mutex[i],NULL);
        io_threads_pending[i] = 0;
        pthread_mutex_lock(&io_threads_mutex[i]); /* Thread will be stopped. */
        if (pthread_create(&tid,NULL,IOThreadMain,(void*)(long)i) != 0) {
            serverLog(LL_WARNING,"Fatal: Can't initialize IO thread.");
            exit(1);
        }
        io_threads[i] = tid;
    }
}

void *IOThreadMain(void *myid) {
    /* The ID is the thread number (from 0 to server.iothreads_num-1), and is
     * used by the thread to just manipulate a single sub-array of clients. */
    long id = (unsigned long)myid;
    char thdname[16];
   
    snprintf(thdname, sizeof(thdname), "io_thd_%ld", id);
    redis_set_thread_title(thdname);
    redisSetCpuAffinity(server.server_cpulist);
   
    while(1) {
        /* Wait for start */
        for (int j = 0; j < 1000000; j++) {
            if (io_threads_pending[id] != 0) break;
        }
       
        /* Give the main thread a chance to stop this thread. */
        if (io_threads_pending[id] == 0) {
            pthread_mutex_lock(&io_threads_mutex[id]);
            pthread_mutex_unlock(&io_threads_mutex[id]);
            continue;
        }
       
        serverAssert(io_threads_pending[id] != 0);
        
        if (tio_debug) printf("[%ld] %d to handle\n", id, (int)listLength(io_threads_list[id]));
        
        /* Process: note that the main thread will never touch our list
         * before we drop the pending count to 0. */
        listIter li;
        listNode *ln;
        listRewind(io_threads_list[id],&li);
        while((ln = listNext(&li))) {
            client *c = listNodeValue(ln);
            if (io_threads_op == IO_THREADS_OP_WRITE) {
                writeToClient(c,0);
            } else if (io_threads_op == IO_THREADS_OP_READ) {
                readQueryFromClient(c->conn);
            } else {
                serverPanic("io_threads_op value is unknown");
            }
        }
        listEmpty(io_threads_list[id]);
        io_threads_pending[id] = 0;
       
        if (tio_debug) printf("[%ld] Done\n", id);
    }
}

void readQueryFromClient(connection *conn) {
    client *c = connGetPrivateData(conn);
    int nread, readlen;
    size_t qblen;
    
    /* Check if we want to read from the client later when exiting from
     * the event loop. This is the case if threaded I/O is enabled. */
    if (postponeClientRead(c)) return;
    ......以下省略
}

/* Return 1 if we want to handle the client read later using threaded I/O.
 * This is called by the readable handler of the event loop.
 * As a side effect of calling this function the client is put in the
 * pending read clients and flagged as such. */
int postponeClientRead(client *c) {
    if (io_threads_active &&
        server.io_threads_do_reads &&
        !ProcessingEventsWhileBlocked &&
        !(c->flags & (CLIENT_MASTER|CLIENT_SLAVE|CLIENT_PENDING_READ)))
    {
        c->flags |= CLIENT_PENDING_READ;
        listAddNodeHead(server.clients_pending_read,c);
        return 1;
    } else {
        return 0;
    }
}

/* When threaded I/O is also enabled for the reading + parsing side, the
 * readable handler will just put normal clients into a queue of clients to
 * process (instead of serving them synchronously). This function runs
 * the queue using the I/O threads, and process them in order to accumulate
 * the reads in the buffers, and also parse the first command available
 * rendering it in the client structures. */
int handleClientsWithPendingReadsUsingThreads(void) {
    if (!io_threads_active || !server.io_threads_do_reads) return 0;
    int processed = listLength(server.clients_pending_read);
    if (processed == 0) return 0;
   
    if (tio_debug) printf("%d TOTAL READ pending clients\n", processed);
   
    /* Distribute the clients across N different lists. */
    listIter li;
    listNode *ln;
    listRewind(server.clients_pending_read,&li);
    int item_id = 0;
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        int target_id = item_id % server.io_threads_num;
        listAddNodeTail(io_threads_list[target_id],c);
        item_id++;
    }
    
    /* Give the start condition to the waiting threads, by setting the
     * start condition atomic var. */
    io_threads_op = IO_THREADS_OP_READ;
    for (int j = 1; j < server.io_threads_num; j++) {
        int count = listLength(io_threads_list[j]);
        io_threads_pending[j] = count;
    }
   
    /* Also use the main thread to process a slice of clients. */
    listRewind(io_threads_list[0],&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        readQueryFromClient(c->conn);
    }
    listEmpty(io_threads_list[0]);
    
    /* Wait for all the other threads to end their work. */
    while(1) {
        unsigned long pending = 0;
        for (int j = 1; j < server.io_threads_num; j++)
            pending += io_threads_pending[j];
        if (pending == 0) break;
    }
    if (tio_debug) printf("I/O READ All threads finshed\n");
   
    /* Run the list of clients again to process the new buffers. */
    while(listLength(server.clients_pending_read)) {
        ln = listFirst(server.clients_pending_read);
        client *c = listNodeValue(ln);
        c->flags &= ~CLIENT_PENDING_READ;
        listDelNode(server.clients_pending_read,ln);
        
        if (c->flags & CLIENT_PENDING_COMMAND) {
            c->flags &= ~CLIENT_PENDING_COMMAND;
            if (processCommandAndResetClient(c) == C_ERR) {
                /* If the client is no longer valid, we avoid
                 * processing the client later. So we just go
                 * to the next. */
                continue;
            }
        }
        processInputBuffer(c);
    }
    return processed;
}

            ......省略
/* If we are in the context of an I/O thread, we can't really
             * execute the command here. All we can do is to flag the client
             * as one that needs to process the command. */
            if (c->flags & CLIENT_PENDING_READ) {
                c->flags |= CLIENT_PENDING_COMMAND;
                break;
            }
            ...... 省略

void clientInstallWriteHandler(client *c) {
    /* Schedule the client to write the output buffers to the socket only
     * if not already done and, for slaves, if the slave can actually receive
     * writes at this stage. */
    if (!(c->flags & CLIENT_PENDING_WRITE) &&
        (c->replstate == REPL_STATE_NONE ||
         (c->replstate == SLAVE_STATE_ONLINE && !c->repl_put_online_on_ack)))
    {
        /* Here instead of installing the write handler, we just flag the
         * client and put it into a list of clients that have something
         * to write to the socket. This way before re-entering the event
         * loop, we can try to directly write to the client sockets avoiding
         * a system call. We'll only really install the write handler if
         * we'll not be able to write the whole reply at once. */
        c->flags |= CLIENT_PENDING_WRITE;
        listAddNodeHead(server.clients_pending_write,c);
    }
}

int handleClientsWithPendingWritesUsingThreads(void) {
    int processed = listLength(server.clients_pending_write);
    if (processed == 0) return 0; /* Return ASAP if there are no clients. */
    
    /* If I/O threads are disabled or we have few clients to serve, don't
     * use I/O threads, but thejboring synchronous code. */
    if (server.io_threads_num == 1 || stopThreadedIOIfNeeded()) {
        return handleClientsWithPendingWrites();
    }
    
    /* Start threads if needed. */
    if (!io_threads_active) startThreadedIO();
   
    if (tio_debug) printf("%d TOTAL WRITE pending clients\n", processed);
    
    /* Distribute the clients across N different lists. */
    listIter li;
    listNode *ln;
    listRewind(server.clients_pending_write,&li);
    int item_id = 0;
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        c->flags &= ~CLIENT_PENDING_WRITE;
        int target_id = item_id % server.io_threads_num;
        listAddNodeTail(io_threads_list[target_id],c);
        item_id++;
    }
   
    /* Give the start condition to the waiting threads, by setting the
     * start condition atomic var. */
    io_threads_op = IO_THREADS_OP_WRITE;
    for (int j = 1; j < server.io_threads_num; j++) {
        int count = listLength(io_threads_list[j]);
        io_threads_pending[j] = count;
    }
    
    /* Also use the main thread to process a slice of clients. */
    listRewind(io_threads_list[0],&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        writeToClient(c,0);
    }
    listEmpty(io_threads_list[0]);
   
    /* Wait for all the other threads to end their work. */
    while(1) {
        unsigned long pending = 0;
        for (int j = 1; j < server.io_threads_num; j++)
            pending += io_threads_pending[j];
        if (pending == 0) break;
    }
    if (tio_debug) printf("I/O WRITE All threads finshed\n");
    
    /* Run the list of clients again to install the write handler where
     * needed. */
    listRewind(server.clients_pending_write,&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
       
        /* Install the write handler if there are pending writes in some
         * of the clients. */
        if (clientHasPendingReplies(c) &&
                connSetWriteHandler(c->conn, sendReplyToClient) == AE_ERR)
        {
            freeClientAsync(c);
        }
    }
    listEmpty(server.clients_pending_write);
    return processed;
}

int stopThreadedIOIfNeeded(void) {
    int pending = listLength(server.clients_pending_write);
    
    /* Return ASAP if IO threads are disabled (single threaded mode). */
    if (server.io_threads_num == 1) return 1;
   
    if (pending < (server.io_threads_num*2)) {
        if (io_threads_active) stopThreadedIO();
        return 1;
    } else {
        return 0;
    }
}

void startThreadedIO(void) {
    serverAssert(server.io_threads_active == 0);
    for (int j = 1; j < server.io_threads_num; j++)
        pthread_mutex_unlock(&io_threads_mutex[j]);
    server.io_threads_active = 1;
}

void stopThreadedIO(void) {
    /* We may have still clients with pending reads when this function
     * is called: handle them before stopping the threads. */
    handleClientsWithPendingReadsUsingThreads();
    serverAssert(server.io_threads_active == 1);
    for (int j = 1; j < server.io_threads_num; j++)
        pthread_mutex_lock(&io_threads_mutex[j]);
    server.io_threads_active = 0;
}

redis-benchmark -h 172.xx.xx.xx -t set,get -n 1000000 -r 100000000 --threads ${threadsize} -d ${datasize} -c ${clientsize}

单线程 threadsize 为 1，多线程 threadsize 为 4
datasize为value 大小，分别设置为 128/512/1024
clientsize 为客户端数量，分别设置为 256/2000
如：./redis-benchmark -h 172.xx.xx.xx -t set,get -n 1000000 -r 100000000 --threads 4 -d 1024 -c 256

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