[PATCH v4 02/19] eal/linux: remove use of VLAs

[Andre Muezerie <andremue@linux.microsoft.com>]

From: Konstantin Ananyev <konstantin.ananyev@huawei.com>

1) ./lib/eal/linux/eal_interrupts.c:1073:16
    : warning: ISO C90 forbids variable length array ‘events’

eal_intr_handle_interrupts() is called by eal_intr_thread_main()
so it seems ok to simply alloc space for events from heap and reuse the
same buffer through the life of the thread.

2) ./lib/eal/linux/eal_interrupts.c:1319:16
    : warning: ISO C90 forbids variable length array ‘evs’

make eal_epoll_wait() use a fixed size array and use it though multiple
iterations to process up to @maxevents events.
Note that technically it is not one to one replacement, as here we might
reduce number of events returned by first call to epoll_wait(..., timeout);

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
---
 lib/eal/linux/eal_interrupts.c | 59 ++++++++++++++++++++++++++++++----
 1 file changed, 52 insertions(+), 7 deletions(-)

diff --git a/lib/eal/linux/eal_interrupts.c b/lib/eal/linux/eal_interrupts.c
index 6436f796eb..d62bb80a3e 100644
--- a/lib/eal/linux/eal_interrupts.c
+++ b/lib/eal/linux/eal_interrupts.c
@@ -34,6 +34,8 @@
 #define EAL_INTR_EPOLL_WAIT_FOREVER (-1)
 #define NB_OTHER_INTR               1
 
+#define MAX_ITER_EVNUM	RTE_EVENT_ETH_INTR_RING_SIZE
+
 static RTE_DEFINE_PER_LCORE(int, _epfd) = -1; /**< epoll fd per thread */
 
 /**
@@ -1068,9 +1070,9 @@ eal_intr_process_interrupts(struct epoll_event *events, int nfds)
  *  void
  */
 static void
-eal_intr_handle_interrupts(int pfd, unsigned totalfds)
+eal_intr_handle_interrupts(int pfd, struct epoll_event events[],
+	unsigned int totalfds)
 {
-	struct epoll_event events[totalfds];
 	int nfds = 0;
 
 	for(;;) {
@@ -1106,6 +1108,12 @@ eal_intr_handle_interrupts(int pfd, unsigned totalfds)
 static __rte_noreturn uint32_t
 eal_intr_thread_main(__rte_unused void *arg)
 {
+	uint32_t n, nb_event;
+	struct epoll_event *events, *p;
+
+	nb_event = 0;
+	events = NULL;
+
 	/* host thread, never break out */
 	for (;;) {
 		/* build up the epoll fd with all descriptors we are to
@@ -1159,8 +1167,23 @@ eal_intr_thread_main(__rte_unused void *arg)
 				numfds++;
 		}
 		rte_spinlock_unlock(&intr_lock);
+
+		/* alloc space for events, when necessary */
+		if (numfds > nb_event) {
+			n = numfds + MAX_ITER_EVNUM;
+			p = realloc(events, n * sizeof(events[0]));
+			if (p == NULL) {
+				EAL_LOG(ERR, "failed to allocate %u events",
+					numfds);
+				numfds = nb_event;
+			} else {
+				nb_event = n;
+				events = p;
+			}
+		}
+
 		/* serve the interrupt */
-		eal_intr_handle_interrupts(pfd, numfds);
+		eal_intr_handle_interrupts(pfd, events, numfds);
 
 		/**
 		 * when we return, we need to rebuild the
@@ -1168,6 +1191,8 @@ eal_intr_thread_main(__rte_unused void *arg)
 		 */
 		close(pfd);
 	}
+
+	free(events);
 }
 
 int
@@ -1316,8 +1341,9 @@ static int
 eal_epoll_wait(int epfd, struct rte_epoll_event *events,
 	       int maxevents, int timeout, bool interruptible)
 {
-	struct epoll_event evs[maxevents];
 	int rc;
+	uint32_t i, k, n, num;
+	struct epoll_event evs[MAX_ITER_EVNUM];
 
 	if (!events) {
 		EAL_LOG(ERR, "rte_epoll_event can't be NULL");
@@ -1328,12 +1354,31 @@ eal_epoll_wait(int epfd, struct rte_epoll_event *events,
 	if (epfd == RTE_EPOLL_PER_THREAD)
 		epfd = rte_intr_tls_epfd();
 
+	num = maxevents;
+	n = RTE_MIN(RTE_DIM(evs), num);
+
+	/* Process events in chunks of MAX_ITER_EVNUM */
+
 	while (1) {
-		rc = epoll_wait(epfd, evs, maxevents, timeout);
+		rc = epoll_wait(epfd, evs, n, timeout);
 		if (likely(rc > 0)) {
+
 			/* epoll_wait has at least one fd ready to read */
-			rc = eal_epoll_process_event(evs, rc, events);
-			break;
+			for (i = 0, k = 0; rc > 0;) {
+				k += rc;
+				rc = eal_epoll_process_event(evs, rc,
+						events + i);
+				i += rc;
+
+				/*
+				 * try to read more events that are already
+				 * available (up to maxevents in total).
+				 */
+				n = RTE_MIN(RTE_DIM(evs), num - k);
+				rc = (n == 0) ? 0 : epoll_wait(epfd, evs, n, 0);
+			}
+			return i;
+
 		} else if (rc < 0) {
 			if (errno == EINTR) {
 				if (interruptible)
-- 
2.34.1