[ovs-dev] [PATCH v2] netdev-linux: Replace sendmsg with sendmmsg in netdev_linux_send

Zhenyu Gao sysugaozhenyu at gmail.com
Tue Jun 20 10:15:34 UTC 2017


Sendmmsg can reduce cpu cycles in sending packets to kernel.
Replace sendmsg with sendmmsg in function netdev_linux_send to send
batch packets if sendmmsg is available.

If kernel side doesn't support sendmmsg, will fallback to sendmsg.

    netserver
|------------|
|            |
|  container |
|----veth----|
          |
          |        |------------|
          |---veth-|   dpdk-ovs |      netperf
                   |            |  |--------------|
                   |----dpdk----|  | bare-metal   |
                         |         |--------------|
                         |              |
                         |              |
                        pnic-----------pnic

Netperf was consumed to test the performance:

1)cmd:netperf -H remote-container -t UDP_STREAM -l 60 -- -m 1400
result: netserver received 2383.21Mb(sendmsg)/2551.64Mb(sendmmsg)

2)cmd:netperf -H remote-container -t UDP_STREAM -l 60 -- -m 60
result: netserver received 109.72Mb(sendmsg)/115.18Mb(sendmmsg)

Sendmmsg show about 6% improvement in netperf UDP testing.

Signed-off-by: Zhenyu Gao <sysugaozhenyu at gmail.com>
---
 configure.ac       |  2 +-
 lib/netdev-linux.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index 6404b5f..b02c7c4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -106,7 +106,7 @@ AC_CHECK_DECLS([sys_siglist], [], [], [[#include <signal.h>]])
 AC_CHECK_MEMBERS([struct stat.st_mtim.tv_nsec, struct stat.st_mtimensec],
   [], [], [[#include <sys/stat.h>]])
 AC_CHECK_MEMBERS([struct ifreq.ifr_flagshigh], [], [], [[#include <net/if.h>]])
-AC_CHECK_FUNCS([mlockall strnlen getloadavg statvfs getmntent_r])
+AC_CHECK_FUNCS([mlockall strnlen getloadavg statvfs getmntent_r sendmmsg])
 AC_CHECK_HEADERS([mntent.h sys/statvfs.h linux/types.h linux/if_ether.h stdatomic.h])
 AC_CHECK_HEADERS([net/if_mib.h], [], [], [[#include <sys/types.h>
 #include <net/if.h>]])
diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
index 1b88775..b90a22a 100644
--- a/lib/netdev-linux.c
+++ b/lib/netdev-linux.c
@@ -1187,6 +1187,54 @@ netdev_linux_rxq_drain(struct netdev_rxq *rxq_)
     }
 }
 
+static inline int
+netdev_linux_sock_batch_send(int sock, struct msghdr *msg,
+                             struct dp_packet_batch *batch)
+{
+    int error = 0;
+    ssize_t retval;
+    uint32_t resend_idx = 0;
+    struct mmsghdr *mmsg;
+    struct iovec *iov;
+
+    mmsg = xmalloc(sizeof(*mmsg) * batch->count);
+    iov = xmalloc(sizeof(*iov) * batch->count);
+
+    for (int i = 0; i < batch->count; i++) {
+        const void *data = dp_packet_data(batch->packets[i]);
+        size_t size = dp_packet_size(batch->packets[i]);
+
+        /* Truncate the packet if it is configured. */
+        size -= dp_packet_get_cutlen(batch->packets[i]);
+
+        iov[i].iov_base = CONST_CAST(void *, data);
+        iov[i].iov_len = size;
+        mmsg[i].msg_hdr = *msg;
+        mmsg[i].msg_hdr.msg_iov = &iov[i];
+    }
+
+resend_batch:
+    retval = sendmmsg(sock, mmsg + resend_idx,
+                      batch->count - resend_idx, 0);
+    if (retval < 0) {
+        if (errno == EINTR) {
+            goto resend_batch;
+        }
+        /* The Linux AF_PACKET implementation never blocks waiting for
+         * room for packets, instead returning ENOBUFS.  Translate this
+         * into EAGAIN for the caller. */
+        error = errno == ENOBUFS ? EAGAIN : errno;
+    } else if (retval != batch->count - resend_idx) {
+       /* Send remain packets again. */
+        resend_idx += retval;
+        goto resend_batch;
+    }
+
+    free(mmsg);
+    free(iov);
+    return error;
+}
+
 /* Sends 'buffer' on 'netdev'.  Returns 0 if successful, otherwise a positive
  * errno value.  Returns EAGAIN without blocking if the packet cannot be queued
  * immediately.  Returns EMSGSIZE if a partial packet was transmitted or if
@@ -1207,6 +1255,9 @@ netdev_linux_send(struct netdev *netdev_, int qid OVS_UNUSED,
     struct sockaddr_ll sll;
     struct msghdr msg;
     if (!is_tap_netdev(netdev_)) {
+#ifdef HAVE_SENDMMSG
+        static bool try_sendmmsg = true;
+#endif
         sock = af_packet_sock();
         if (sock < 0) {
             error = -sock;
@@ -1231,6 +1282,21 @@ netdev_linux_send(struct netdev *netdev_, int qid OVS_UNUSED,
         msg.msg_control = NULL;
         msg.msg_controllen = 0;
         msg.msg_flags = 0;
+
+#ifdef HAVE_SENDMMSG
+        if (try_sendmmsg) {
+            /* Try batch sending to socket */
+            error = netdev_linux_sock_batch_send(sock, &msg, batch);
+            if (error == ENOSYS) {
+                /* Linux kernel does not implement this function */
+                try_sendmmsg = false;
+                VLOG_WARN("Linux kernel doesn't implement sendmmsg, "
+                          "going to consume sendmsg");
+            } else {
+                goto check_error;
+            }
+        }
+#endif
     }
 
     /* 'i' is incremented only if there's no error */
@@ -1290,9 +1356,10 @@ netdev_linux_send(struct netdev *netdev_, int qid OVS_UNUSED,
         i++;
     }
 
+check_error:
     if (error && error != EAGAIN) {
-            VLOG_WARN_RL(&rl, "error sending Ethernet packet on %s: %s",
-                         netdev_get_name(netdev_), ovs_strerror(error));
+        VLOG_WARN_RL(&rl, "error sending Ethernet packet on %s: %s",
+                     netdev_get_name(netdev_), ovs_strerror(error));
     }
 
 free_batch:
-- 
1.8.3.1



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