4 files changed, 36 insertions, 0 deletions
diff --git a/nbd/client-connection.c b/nbd/client-connection.c
index b11e266..79ea97e 100644
--- a/nbd/client-connection.c
+++ b/nbd/client-connection.c
@@ -31,6 +31,8 @@
 #include "qapi/clone-visitor.h"
 #include "qemu/coroutine.h"
 
+#include "nbd/nbd-internal.h"
+
 struct NBDClientConnection {
     /* Initialization constants, never change */
     SocketAddress *saddr; /* address to connect to */
@@ -140,6 +142,7 @@ static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
         return ret;
     }
 
+    nbd_set_socket_send_buffer(sioc);
     qio_channel_set_delay(QIO_CHANNEL(sioc), false);
 
     if (!info) {
diff --git a/nbd/common.c b/nbd/common.c
index 589a748..2a133a6 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -18,6 +18,9 @@
 
 #include "qemu/osdep.h"
 #include "trace.h"
+#include "io/channel-socket.h"
+#include "qapi/error.h"
+#include "qemu/units.h"
 #include "nbd-internal.h"
 
 /* Discard length bytes from channel.  Return -errno on failure and 0 on
@@ -264,3 +267,26 @@ const char *nbd_mode_lookup(NBDMode mode)
         return "<unknown>";
     }
 }
+
+/*
+ * Testing shows that 2m send buffer is optimal. Changing the receive buffer
+ * size has no effect on performance.
+ * On Linux we need to increase net.core.wmem_max to make this effective.
+ */
+#if defined(__APPLE__) || defined(__linux__)
+#define UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE (2 * MiB)
+#endif
+
+void nbd_set_socket_send_buffer(QIOChannelSocket *sioc)
+{
+#ifdef UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE
+    if (sioc->localAddr.ss_family == AF_UNIX) {
+        size_t size = UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE;
+        Error *errp = NULL;
+
+        if (qio_channel_socket_set_send_buffer(sioc, size, &errp) < 0) {
+            warn_report_err(errp);
+        }
+    }
+#endif /* UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE */
+}
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index 715d92d..6bafeef 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -74,4 +74,9 @@ static inline int nbd_write(QIOChannel *ioc, const void *buffer, size_t size,
 
 int nbd_drop(QIOChannel *ioc, size_t size, Error **errp);
 
+/* nbd_set_socket_send_buffer
+ * Set the socket send buffer size for optimal performance.
+ */
+void nbd_set_socket_send_buffer(QIOChannelSocket *sioc);
+
 #endif
diff --git a/nbd/server.c b/nbd/server.c
index 2076fb2..d242be9 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -3291,6 +3291,8 @@ void nbd_client_new(QIOChannelSocket *sioc,
     client->close_fn = close_fn;
     client->owner = owner;
 
+    nbd_set_socket_send_buffer(sioc);
+
     co = qemu_coroutine_create(nbd_co_client_start, client);
     qemu_coroutine_enter(co);
 }