On macOS we need to increase unix stream socket buffers size on the
client and server to get good performance. We set socket buffers on
macOS after connecting or accepting a client connection. For unix
datagram socket we need different configuration that can be done later.
Testing shows that setting socket receive buffer size (SO_RCVBUF) has no
effect on performance, so we set only the send buffer size (SO_SNDBUF).
It seems to work like Linux but not documented.
Testing shows that optimal buffer size is 512k to 4 MiB, depending on
the test case. The difference is very small, so I chose 2 MiB.
I tested reading from qemu-nbd and writing to qemu-nbd with qemu-img and
computing a blkhash with nbdcopy and blksum.
To focus on NBD communication and get less noisy results, I tested
reading and writing to null-co driver. I added a read-pattern option to
the null-co driver to return data full of 0xff:
NULL="json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size': '10g',
'read-pattern': -1}}"
For testing buffer size I added an environment variable for setting the
socket buffer size.
Read from qemu-nbd via qemu-img convert. In this test buffer size of 2m
is optimal (12.6 times faster).
qemu-nbd -r -t -e 0 -f raw -k /tmp/nbd.sock "$NULL" &
qemu-img convert -f raw -O raw -W -n "nbd+unix:///?socket=/tmp/nbd.sock"
"$NULL"
| buffer size | time | user | system |
|-------------|---------|---------|---------|
| default | 13.361 | 2.653 | 5.702 |
| 65536 | 2.283 | 0.204 | 1.318 |
| 131072 | 1.673 | 0.062 | 1.008 |
| 262144 | 1.592 | 0.053 | 0.952 |
| 524288 | 1.496 | 0.049 | 0.887 |
| 1048576 | 1.234 | 0.047 | 0.738 |
| 2097152 | 1.060 | 0.080 | 0.602 |
| 4194304 | 1.061 | 0.076 | 0.604 |
Write to qemu-nbd with qemu-img convert. In this test buffer size of 2m
is optimal (9.2 times faster).
qemu-nbd -t -e 0 -f raw -k /tmp/nbd.sock "$NULL" &
qemu-img convert -f raw -O raw -W -n "$NULL"
"nbd+unix:///?socket=/tmp/nbd.sock"
| buffer size | time | user | system |
|-------------|---------|---------|---------|
| default | 8.063 | 2.522 | 4.184 |
| 65536 | 1.472 | 0.430 | 0.867 |
| 131072 | 1.071 | 0.297 | 0.654 |
| 262144 | 1.012 | 0.239 | 0.587 |
| 524288 | 0.970 | 0.201 | 0.514 |
| 1048576 | 0.895 | 0.184 | 0.454 |
| 2097152 | 0.877 | 0.174 | 0.440 |
| 4194304 | 0.944 | 0.231 | 0.535 |
Compute a blkhash with nbdcopy, using 4 NBD connections and 256k request
size. In this test buffer size of 4m is optimal (5.1 times faster).
qemu-nbd -r -t -e 0 -f raw -k /tmp/nbd.sock "$NULL" &
nbdcopy --blkhash "nbd+unix:///?socket=/tmp/nbd.sock" null:
| buffer size | time | user | system |
|-------------|---------|---------|---------|
| default | 8.624 | 5.727 | 6.507 |
| 65536 | 2.563 | 4.760 | 2.498 |
| 131072 | 1.903 | 4.559 | 2.093 |
| 262144 | 1.759 | 4.513 | 1.935 |
| 524288 | 1.729 | 4.489 | 1.924 |
| 1048576 | 1.696 | 4.479 | 1.884 |
| 2097152 | 1.710 | 4.480 | 1.763 |
| 4194304 | 1.687 | 4.479 | 1.712 |
Compute a blkhash with blksum, using 1 NBD connection and 256k read
size. In this test buffer size of 512k is optimal (10.3 times faster).
qemu-nbd -r -t -e 0 -f raw -k /tmp/nbd.sock "$NULL" &
blksum "nbd+unix:///?socket=/tmp/nbd.sock"
| buffer size | time | user | system |
|-------------|---------|---------|---------|
| default | 13.085 | 5.664 | 6.461 |
| 65536 | 3.299 | 5.106 | 2.515 |
| 131072 | 2.396 | 4.989 | 2.069 |
| 262144 | 1.607 | 4.724 | 1.555 |
| 524288 | 1.271 | 4.528 | 1.224 |
| 1048576 | 1.294 | 4.565 | 1.333 |
| 2097152 | 1.299 | 4.569 | 1.344 |
| 4194304 | 1.291 | 4.559 | 1.327 |
Signed-off-by: Nir Soffer <nir...@gmail.com>
---
io/channel-socket.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/io/channel-socket.c b/io/channel-socket.c
index 608bcf066e..06901ab694 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -21,6 +21,7 @@
#include "qapi/error.h"
#include "qapi/qapi-visit-sockets.h"
#include "qemu/module.h"
+#include "qemu/units.h"
#include "io/channel-socket.h"
#include "io/channel-util.h"
#include "io/channel-watch.h"
@@ -37,6 +38,33 @@
#define SOCKET_MAX_FDS 16
+/*
+ * Testing shows that 2m send buffer gives best throuput and lowest cpu usage.
+ * Changing the receive buffer size has no effect on performance.
+ */
+#ifdef __APPLE__
+#define UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE (2 * MiB)
+#endif /* __APPLE__ */
+
+static void qio_channel_socket_set_buffers(QIOChannelSocket *ioc)
+{
+ if (ioc->localAddr.ss_family == AF_UNIX) {
+ int type;
+ socklen_t type_len = sizeof(type);
+
+ if (getsockopt(ioc->fd, SOL_SOCKET, SO_TYPE, &type, &type_len) == -1) {
+ return;
+ }
+
+#ifdef UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE
+ if (type == SOCK_STREAM) {
+ const int value = UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE;
+ setsockopt(ioc->fd, SOL_SOCKET, SO_SNDBUF, &value, sizeof(value));
+ }
+#endif /* UNIX_STREAM_SOCKET_SEND_BUFFER_SIZE */
+ }
+}
+
SocketAddress *
qio_channel_socket_get_local_address(QIOChannelSocket *ioc,
Error **errp)
@@ -174,6 +202,8 @@ int qio_channel_socket_connect_sync(QIOChannelSocket *ioc,
}
#endif
+ qio_channel_socket_set_buffers(ioc);
+
qio_channel_set_feature(QIO_CHANNEL(ioc),
QIO_CHANNEL_FEATURE_READ_MSG_PEEK);
@@ -410,6 +440,8 @@ qio_channel_socket_accept(QIOChannelSocket *ioc,
}
#endif /* WIN32 */
+ qio_channel_socket_set_buffers(cioc);
+
qio_channel_set_feature(QIO_CHANNEL(cioc),
QIO_CHANNEL_FEATURE_READ_MSG_PEEK);
--
2.39.5 (Apple Git-154)
