[dpdk-dev] [PATCH 2/2] vhost: add pipe event for optimizing negotiating

[xiangxia.m.yue@gmail.com]

From: Tonghao Zhang <xiangxia.m.yue@gmail.com>

When vhost—user connects qemu successfully, dpdk will call
the vhost_user_add_connection to add unix socket fd to poll.
And fdset_add only set the socket fd to a fdentry while poll
may sleep now. In a general case, this is no problem. But if
we use hot update for vhost-user, most downtime of VMs network
is 750+ms. This patch adds pipe event, so after connections are
ok, dpdk rebuild the poll immediately. With this patch, the
most downtime is 20~30ms.

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
---
 lib/librte_vhost/fd_man.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 lib/librte_vhost/fd_man.h | 16 ++++++++++++++++
 lib/librte_vhost/socket.c | 14 ++++++++++++++
 3 files changed, 79 insertions(+)

diff --git a/lib/librte_vhost/fd_man.c b/lib/librte_vhost/fd_man.c
index 181711c..7716757 100644
--- a/lib/librte_vhost/fd_man.c
+++ b/lib/librte_vhost/fd_man.c
@@ -15,6 +15,7 @@
 #include <rte_log.h>
 
 #include "fd_man.h"
+#include "vhost.h"
 
 #define FDPOLLERR (POLLERR | POLLHUP | POLLNVAL)
 
@@ -272,3 +273,51 @@
 
 	return NULL;
 }
+
+static void
+fdset_pipe_read_cb(int readfd, void *dat __rte_unused,
+		   int *remove __rte_unused)
+{
+	char charbuf[16];
+	read(readfd, charbuf, sizeof(charbuf));
+}
+
+void
+fdset_pipe_uninit(struct fdset *fdset)
+{
+	fdset_del(fdset, fdset->u.readfd);
+	close(fdset->u.readfd);
+	close(fdset->u.writefd);
+}
+
+int
+fdset_pipe_init(struct fdset *fdset)
+{
+	int ret;
+
+	if (pipe(fdset->u.pipefd) < 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"failed to create pipe for vhost fdset\n");
+		return -1;
+	}
+
+	ret = fdset_add(fdset, fdset->u.readfd,
+			fdset_pipe_read_cb, NULL, NULL);
+
+	if (ret < 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"failed to add pipe readfd %d into vhost server fdset\n",
+			fdset->u.readfd);
+
+		fdset_pipe_uninit(fdset);
+		return -1;
+	}
+
+	return 0;
+}
+
+void
+fdset_pipe_notify(struct fdset *fdset)
+{
+	write(fdset->u.writefd, "1", 1);
+}
diff --git a/lib/librte_vhost/fd_man.h b/lib/librte_vhost/fd_man.h
index 3a9276c..76a42fb 100644
--- a/lib/librte_vhost/fd_man.h
+++ b/lib/librte_vhost/fd_man.h
@@ -25,6 +25,16 @@ struct fdset {
 	struct fdentry fd[MAX_FDS];
 	pthread_mutex_t fd_mutex;
 	int num;	/* current fd number of this fdset */
+
+	union pipefds {
+		struct {
+			int pipefd[2];
+		};
+		struct {
+			int readfd;
+			int writefd;
+		};
+	} u;
 };
 
 
@@ -37,4 +47,10 @@ int fdset_add(struct fdset *pfdset, int fd,
 
 void *fdset_event_dispatch(void *arg);
 
+int fdset_pipe_init(struct fdset *fdset);
+
+void fdset_pipe_uninit(struct fdset *fdset);
+
+void fdset_pipe_notify(struct fdset *fdset);
+
 #endif
diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 95bed78..795239c 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -231,6 +231,8 @@ struct vhost_user {
 	pthread_mutex_lock(&vsocket->conn_mutex);
 	TAILQ_INSERT_TAIL(&vsocket->conn_list, conn, next);
 	pthread_mutex_unlock(&vsocket->conn_mutex);
+
+	fdset_pipe_notify(&vhost_user.fdset);
 	return;
 
 err:
@@ -829,11 +831,23 @@ struct vhost_device_ops const *
 		return -1;
 
 	if (fdset_tid == 0) {
+		/**
+		 * create a pipe which will be waited by poll and notified to
+		 * rebuild the wait list of poll.
+		 */
+		if (fdset_pipe_init(&vhost_user.fdset) < 0) {
+			RTE_LOG(ERR, VHOST_CONFIG,
+				"failed to create pipe for vhost fdset\n");
+			return -1;
+		}
+
 		int ret = pthread_create(&fdset_tid, NULL, fdset_event_dispatch,
 				     &vhost_user.fdset);
 		if (ret != 0) {
 			RTE_LOG(ERR, VHOST_CONFIG,
 				"failed to create fdset handling thread");
+
+			fdset_pipe_uninit(&vhost_user.fdset);
 			return -1;
 		} else {
 			snprintf(thread_name, RTE_MAX_THREAD_NAME_LEN,
-- 
1.8.3.1