relayd: optimize receive throughput

For channels configured with large sub-buffer size, the relayd copies
the entire trace sub-buffer (trace packet) into a large buffer, and then
copies the large buffer to disk. It is inefficient from a point of view
of cache locality.

Use a 64k buffer on the stack instead, and move the data piece-wise.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 0c7ef8d76c0449afba1aa314cf33db87a3af2368..1ac975660b5ada3a9fe30a2bd5330b22ca1b94aa 100644 (file)
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -83,6 +83,10 @@ static int opt_daemon, opt_background;
  */
 #define NR_LTTNG_RELAY_READY   3
 static int lttng_relay_ready = NR_LTTNG_RELAY_READY;
+
+/* Size of receive buffer. */
+#define RECV_DATA_BUFFER_SIZE          65536
+
 static int recv_child_signal;  /* Set to 1 when a SIGUSR1 signal is received. */
 static pid_t child_ppid;       /* Internal parent PID use with daemonize. */
 
@@ -2166,6 +2170,9 @@ static int relay_process_data(struct relay_connection *conn)
        uint32_t data_size;
        struct relay_session *session;
        bool new_stream = false, close_requested = false;
+       size_t chunk_size = RECV_DATA_BUFFER_SIZE;
+       size_t recv_off = 0;
+       char data_buffer[chunk_size];
 
        ret = conn->sock->ops->recvmsg(conn->sock, &data_hdr,
                        sizeof(struct lttcomm_relayd_data_hdr), 0);
@@ -2189,36 +2196,11 @@ static int relay_process_data(struct relay_connection *conn)
        }
        session = stream->trace->session;
        data_size = be32toh(data_hdr.data_size);
-       if (data_buffer_size < data_size) {
-               char *tmp_data_ptr;
-
-               tmp_data_ptr = realloc(data_buffer, data_size);
-               if (!tmp_data_ptr) {
-                       ERR("Allocating data buffer");
-                       free(data_buffer);
-                       ret = -1;
-                       goto end_stream_put;
-               }
-               data_buffer = tmp_data_ptr;
-               data_buffer_size = data_size;
-       }
-       memset(data_buffer, 0, data_size);
 
        net_seq_num = be64toh(data_hdr.net_seq_num);
 
        DBG3("Receiving data of size %u for stream id %" PRIu64 " seqnum %" PRIu64,
                data_size, stream_id, net_seq_num);
-       ret = conn->sock->ops->recvmsg(conn->sock, data_buffer, data_size, 0);
-       if (ret <= 0) {
-               if (ret == 0) {
-                       /* Orderly shutdown. Not necessary to print an error. */
-                       DBG("Socket %d did an orderly shutdown", conn->sock->fd);
-               } else {
-                       ERR("Socket %d error %d", conn->sock->fd, ret);
-               }
-               ret = -1;
-               goto end_stream_put;
-       }
 
        pthread_mutex_lock(&stream->lock);
 
@@ -2264,16 +2246,33 @@ static int relay_process_data(struct relay_connection *conn)
                }
        }
 
-       /* Write data to stream output fd. */
-       size_ret = lttng_write(stream->stream_fd->fd, data_buffer, data_size);
-       if (size_ret < data_size) {
-               ERR("Relay error writing data to file");
-               ret = -1;
-               goto end_stream_unlock;
-       }
+       for (recv_off = 0; recv_off < data_size; recv_off += chunk_size) {
+               size_t recv_size = min(data_size - recv_off, chunk_size);
 
-       DBG2("Relay wrote %zd bytes to tracefile for stream id %" PRIu64,
-                       size_ret, stream->stream_handle);
+               ret = conn->sock->ops->recvmsg(conn->sock, data_buffer, recv_size, 0);
+               if (ret <= 0) {
+                       if (ret == 0) {
+                               /* Orderly shutdown. Not necessary to print an error. */
+                               DBG("Socket %d did an orderly shutdown", conn->sock->fd);
+                       } else {
+                               ERR("Socket %d error %d", conn->sock->fd, ret);
+                       }
+                       ret = -1;
+                       goto end_stream_unlock;
+               }
+
+               /* Write data to stream output fd. */
+               size_ret = lttng_write(stream->stream_fd->fd, data_buffer,
+                               recv_size);
+               if (size_ret < recv_size) {
+                       ERR("Relay error writing data to file");
+                       ret = -1;
+                       goto end_stream_unlock;
+               }
+
+               DBG2("Relay wrote %zd bytes to tracefile for stream id %" PRIu64,
+                               size_ret, stream->stream_handle);
+       }
 
        ret = write_padding_to_file(stream->stream_fd->fd,
                        be32toh(data_hdr.padding_size));
@@ -2302,7 +2301,6 @@ end_stream_unlock:
                uatomic_set(&session->new_streams, 1);
                pthread_mutex_unlock(&session->lock);
        }
-end_stream_put:
        stream_put(stream);
 end:
        return ret;
@@ -2620,7 +2618,6 @@ relay_connections_ht_error:
                DBG("Thread exited with error");
        }
        DBG("Worker thread cleanup complete");
-       free(data_buffer);
 error_testpoint:
        if (err) {
                health_error();