[dpdk-dev] [PATCH v3] vhost: allow for many vhost user ports

[Jan Wickbom <jan.wickbom@ericsson.com>]

Currently select() is used to monitor file descriptors for vhostuser
ports. This limits the number of ports possible to create since the
fd number is used as index in the fd_set and we have seen fds > 1023.
This patch changes select() to poll(). This way we can keep an
packed (pollfd) array for the fds, e.g. as many fds as the size of
the array.

Also see:
http://dpdk.org/ml/archives/dev/2016-April/037024.html

Signed-off-by: Jan Wickbom <jan.wickbom@ericsson.com>
Reported-by: Patrik Andersson <patrik.r.andersson@ericsson.com>
---

v3:
* removed unnecessary include
* removed fdset_fill, made it functionally part of poll loop

v2:
* removed unnecessary casts
* static array replacing allocated memory

 lib/librte_vhost/fd_man.c | 194 +++++++++++++++++++++++++---------------------
 lib/librte_vhost/fd_man.h |   2 +-
 2 files changed, 105 insertions(+), 91 deletions(-)

diff --git a/lib/librte_vhost/fd_man.c b/lib/librte_vhost/fd_man.c
index 2d3eeb7..c360d07 100644
--- a/lib/librte_vhost/fd_man.c
+++ b/lib/librte_vhost/fd_man.c
@@ -35,16 +35,40 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/socket.h>
-#include <sys/select.h>
 #include <sys/time.h>
 #include <sys/types.h>
+#include <poll.h>
 #include <unistd.h>
+#include <string.h>
 
 #include <rte_common.h>
 #include <rte_log.h>
 
 #include "fd_man.h"
 
+#define FDPOLLERR (POLLERR | POLLHUP | POLLNVAL)
+
+
+static struct pollfd rwfds[MAX_FDS];
+
+/**
+ * Adjusts the highest index populated in the array of fds
+ * @return
+ *   The new size of fdset.
+ */
+static void
+fdset_shrink(struct fdset *pfdset)
+{
+	int idx;
+
+	for (idx = pfdset->num - 1;
+	     idx >= 0 && pfdset->fd[idx].fd == -1;
+	     idx--)
+		;
+
+	pfdset->num = idx + 1;
+}
+
 /**
  * Returns the index in the fdset for a given fd.
  * If fd is -1, it means to search for a free entry.
@@ -56,72 +80,32 @@
 {
 	int i;
 
-	if (pfdset == NULL)
-		return -1;
-
-	for (i = 0; i < MAX_FDS && pfdset->fd[i].fd != fd; i++)
+	for (i = 0; i < pfdset->num && pfdset->fd[i].fd != fd; i++)
 		;
 
-	return i ==  MAX_FDS ? -1 : i;
+	return i == pfdset->num ? -1 : i;
 }
 
 static int
 fdset_find_free_slot(struct fdset *pfdset)
 {
-	return fdset_find_fd(pfdset, -1);
+	if (pfdset->num < MAX_FDS)
+		return pfdset->num;
+	else
+		return fdset_find_fd(pfdset, -1);
 }
 
-static int
-fdset_add_fd(struct fdset  *pfdset, int idx, int fd,
+static void
+fdset_add_fd(struct fdset *pfdset, int idx, int fd,
 	fd_cb rcb, fd_cb wcb, void *dat)
 {
 	struct fdentry *pfdentry;
 
-	if (pfdset == NULL || idx >= MAX_FDS || fd >= FD_SETSIZE)
-		return -1;
-
 	pfdentry = &pfdset->fd[idx];
 	pfdentry->fd = fd;
 	pfdentry->rcb = rcb;
 	pfdentry->wcb = wcb;
 	pfdentry->dat = dat;
-
-	return 0;
-}
-
-/**
- * Fill the read/write fd_set with the fds in the fdset.
- * @return
- *  the maximum fds filled in the read/write fd_set.
- */
-static int
-fdset_fill(fd_set *rfset, fd_set *wfset, struct fdset *pfdset)
-{
-	struct fdentry *pfdentry;
-	int i, maxfds = -1;
-	int num = MAX_FDS;
-
-	if (pfdset == NULL)
-		return -1;
-
-	for (i = 0; i < num; i++) {
-		pfdentry = &pfdset->fd[i];
-		if (pfdentry->fd != -1) {
-			int added = 0;
-			if (pfdentry->rcb && rfset) {
-				FD_SET(pfdentry->fd, rfset);
-				added = 1;
-			}
-			if (pfdentry->wcb && wfset) {
-				FD_SET(pfdentry->fd, wfset);
-				added = 1;
-			}
-			if (added)
-				maxfds = pfdentry->fd < maxfds ?
-					maxfds : pfdentry->fd;
-		}
-	}
-	return maxfds;
 }
 
 void
@@ -132,6 +116,8 @@
 	if (pfdset == NULL)
 		return;
 
+	pthread_mutex_init(&pfdset->fd_mutex, NULL);
+
 	for (i = 0; i < MAX_FDS; i++) {
 		pfdset->fd[i].fd = -1;
 		pfdset->fd[i].dat = NULL;
@@ -152,14 +138,15 @@
 
 	pthread_mutex_lock(&pfdset->fd_mutex);
 
-	/* Find a free slot in the list. */
 	i = fdset_find_free_slot(pfdset);
-	if (i == -1 || fdset_add_fd(pfdset, i, fd, rcb, wcb, dat) < 0) {
+	if (i == -1) {
 		pthread_mutex_unlock(&pfdset->fd_mutex);
 		return -2;
 	}
 
-	pfdset->num++;
+	fdset_add_fd(pfdset, i, fd, rcb, wcb, dat);
+	if (i == pfdset->num)
+		pfdset->num++;
 
 	pthread_mutex_unlock(&pfdset->fd_mutex);
 
@@ -189,7 +176,7 @@
 			pfdset->fd[i].fd = -1;
 			pfdset->fd[i].rcb = pfdset->fd[i].wcb = NULL;
 			pfdset->fd[i].dat = NULL;
-			pfdset->num--;
+			fdset_shrink(pfdset);
 			i = -1;
 		}
 		pthread_mutex_unlock(&pfdset->fd_mutex);
@@ -198,25 +185,26 @@
 	return dat;
 }
 
+
 /**
- *  Unregister the fd at the specified slot from the fdset.
+ *  Moves the fd from last slot to specified slot, including
+ *  corresponding pollfd
  */
 static void
-fdset_del_slot(struct fdset *pfdset, int index)
+fdset_move_last(struct fdset *pfdset, int idx)
 {
-	if (pfdset == NULL || index < 0 || index >= MAX_FDS)
-		return;
-
-	pthread_mutex_lock(&pfdset->fd_mutex);
+	int last_idx = pfdset->num - 1;
 
-	pfdset->fd[index].fd = -1;
-	pfdset->fd[index].rcb = pfdset->fd[index].wcb = NULL;
-	pfdset->fd[index].dat = NULL;
-	pfdset->num--;
+	if (idx < last_idx) {
+		pfdset->fd[idx] = pfdset->fd[last_idx];
+		pfdset->fd[last_idx].fd = -1;
 
-	pthread_mutex_unlock(&pfdset->fd_mutex);
+		rwfds[idx] = rwfds[last_idx];
+		rwfds[last_idx].revents = 0;
+	}
 }
 
+
 /**
  * This functions runs in infinite blocking loop until there is no fd in
  * pfdset. It calls corresponding r/w handler if there is event on the fd.
@@ -229,55 +217,71 @@
 void
 fdset_event_dispatch(struct fdset *pfdset)
 {
-	fd_set rfds, wfds;
-	int i, maxfds;
+	int i;
 	struct fdentry *pfdentry;
-	int num = MAX_FDS;
 	fd_cb rcb, wcb;
 	void *dat;
 	int fd;
 	int remove1, remove2;
-	int ret;
 
 	if (pfdset == NULL)
 		return;
 
-	while (1) {
-		struct timeval tv;
-		tv.tv_sec = 1;
-		tv.tv_usec = 0;
-		FD_ZERO(&rfds);
-		FD_ZERO(&wfds);
-		pthread_mutex_lock(&pfdset->fd_mutex);
-
-		maxfds = fdset_fill(&rfds, &wfds, pfdset);
-
-		pthread_mutex_unlock(&pfdset->fd_mutex);
+	memset(rwfds, 0, sizeof(rwfds));
 
+	while (1) {
 		/*
-		 * When select is blocked, other threads might unregister
+		 * When poll is blocked, other threads might unregister
 		 * listenfds from and register new listenfds into fdset.
-		 * When select returns, the entries for listenfds in the fdset
+		 * When poll returns, the entries for listenfds in the fdset
 		 * might have been updated. It is ok if there is unwanted call
 		 * for new listenfds.
 		 */
-		ret = select(maxfds + 1, &rfds, &wfds, NULL, &tv);
-		if (ret <= 0)
-			continue;
+		poll(rwfds, pfdset->num, 1000 /* millisecs */);
 
-		for (i = 0; i < num; i++) {
-			remove1 = remove2 = 0;
+		for (i = 0; i < pfdset->num; ) {
 			pthread_mutex_lock(&pfdset->fd_mutex);
+
 			pfdentry = &pfdset->fd[i];
 			fd = pfdentry->fd;
+
+			if (fd < 0) {
+				/* Removed during poll */
+
+				fdset_move_last(pfdset, i);
+				fdset_shrink(pfdset);
+
+				pthread_mutex_unlock(&pfdset->fd_mutex);
+
+				continue;
+			}
+
+			if (!rwfds[i].revents) {
+				/* No revents, maybe added during poll */
+
+				rwfds[i].fd = fd;
+				rwfds[i].events = pfdentry->rcb ? POLLIN : 0;
+				rwfds[i].events |= pfdentry->wcb ? POLLOUT : 0;
+				pthread_mutex_unlock(&pfdset->fd_mutex);
+
+				i++;
+				continue;
+			}
+
+			/* Valid fd, and at least one revent ... */
+
+			remove1 = remove2 = 0;
+
 			rcb = pfdentry->rcb;
 			wcb = pfdentry->wcb;
 			dat = pfdentry->dat;
 			pfdentry->busy = 1;
+
 			pthread_mutex_unlock(&pfdset->fd_mutex);
-			if (fd >= 0 && FD_ISSET(fd, &rfds) && rcb)
+
+			if (rcb && rwfds[i].revents & (POLLIN | FDPOLLERR))
 				rcb(fd, dat, &remove1);
-			if (fd >= 0 && FD_ISSET(fd, &wfds) && wcb)
+			if (wcb && rwfds[i].revents & (POLLOUT | FDPOLLERR))
 				wcb(fd, dat, &remove2);
 			pfdentry->busy = 0;
 			/*
@@ -292,8 +296,18 @@
 			 * listen fd in another thread, we couldn't call
 			 * fd_set_del.
 			 */
-			if (remove1 || remove2)
-				fdset_del_slot(pfdset, i);
+			if (remove1 || remove2) {
+				pthread_mutex_lock(&pfdset->fd_mutex);
+
+				fdset_move_last(pfdset, i);
+				fdset_shrink(pfdset);
+
+				pthread_mutex_unlock(&pfdset->fd_mutex);
+
+				continue;
+			}
+
+			i++;
 		}
 	}
 }
diff --git a/lib/librte_vhost/fd_man.h b/lib/librte_vhost/fd_man.h
index bd66ed1..b5ba688 100644
--- a/lib/librte_vhost/fd_man.h
+++ b/lib/librte_vhost/fd_man.h
@@ -51,7 +51,7 @@ struct fdentry {
 struct fdset {
 	struct fdentry fd[MAX_FDS];
 	pthread_mutex_t fd_mutex;
-	int num;	/* current fd number of this fdset */
+	int num;	/* highest index occupied in fd array + 1 */
 };
 
 
-- 
1.9.1