From: Nir Soffer Date: Sat, 17 May 2025 20:11:53 +0000 (+0300) Subject: nbd: Set unix socket send buffer on macOS X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e9f4550b74a8a9774979a51caa4b1aaff9e1d055;p=thirdparty%2Fqemu.git nbd: Set unix socket send buffer on macOS On macOS we need to increase unix 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. 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': 255}}" 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 Message-ID: <20250517201154.88456-3-nirsof@gmail.com> Reviewed-by: Daniel P. Berrangé Signed-off-by: Eric Blake --- diff --git a/nbd/client-connection.c b/nbd/client-connection.c index b11e266807..79ea97e4cc 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 589a748cfe..9436e9d1d1 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 +267,25 @@ const char *nbd_mode_lookup(NBDMode mode) return ""; } } + +/* + * Testing shows that 2m send buffer is optimal. Changing the receive buffer + * size has no effect on performance. + */ +#if defined(__APPLE__) +#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 715d92d6ef..6bafeef5dd 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 2076fb2666..d242be9811 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); }