sysmobts: Use writev for the outgoing data of the write queue

Attempt to write multiple primitives at the same time instead of
the select/write, select/write that is currently done. The queue
size is big enough to hold several entries at the same time and it
is unlikely we get the -EAGAIN from the kernel driver.

The writev code works by assuming that each element in the queue
has the same size. This is not verified by the code and if this
assumption breaks at some point the code will drop primitives or
send some twice.

1 files changed, 69 insertions, 0 deletions

diff --git a/src/osmo-bts-sysmo/l1_transp_hw.c b/src/osmo-bts-sysmo/l1_transp_hw.c
index 4db4b30b..f0f028bb 100644
--- a/src/osmo-bts-sysmo/l1_transp_hw.c
+++ b/src/osmo-bts-sysmo/l1_transp_hw.c
@@ -88,6 +88,74 @@ static const char *wr_devnames[] = {
 osmo_static_assert(sizeof(GsmL1_Prim_t) + 128 <= SYSMOBTS_PRIM_SIZE, l1_prim)
 osmo_static_assert(sizeof(SuperFemto_Prim_t) + 128 <= SYSMOBTS_PRIM_SIZE, super_prim)
 
+static int wqueue_vector_cb(struct osmo_fd *fd, unsigned int what)
+{
+	struct osmo_wqueue *queue;
+
+	queue = container_of(fd, struct osmo_wqueue, bfd);
+
+	if (what & BSC_FD_READ)
+		queue->read_cb(fd);
+
+	if (what & BSC_FD_EXCEPT)
+		queue->except_cb(fd);
+
+	if (what & BSC_FD_WRITE) {
+		struct iovec iov[5];
+		struct msgb *msg, *tmp;
+		int written, count = 0;
+
+		fd->when &= ~BSC_FD_WRITE;
+
+		llist_for_each_entry(msg, &queue->msg_queue, list) {
+			/* more writes than we have */
+			if (count >= ARRAY_SIZE(iov))
+				break;
+
+			iov[count].iov_base = msg->l1h;
+			iov[count].iov_len = msgb_l1len(msg);
+			count += 1;
+		}
+
+		/* TODO: check if all lengths are the same. */
+
+
+		/* Nothing scheduled? This should not happen. */
+		if (count == 0) {
+			if (!llist_empty(&queue->msg_queue))
+				fd->when |= BSC_FD_WRITE;
+			return 0;
+		}
+
+		written = writev(fd->fd, iov, count);
+		if (written < 0) {
+			/* nothing written?! */
+			if (!llist_empty(&queue->msg_queue))
+				fd->when |= BSC_FD_WRITE;
+			return 0;
+		}
+
+		/* now delete the written entries */
+		written = written / iov[0].iov_len;
+		count = 0;
+		llist_for_each_entry_safe(msg, tmp, &queue->msg_queue, list) {
+			queue->current_length -= 1;
+
+			llist_del(&msg->list);
+			msgb_free(msg);
+
+			count += 1;
+			if (count >= written)
+				break;
+		}
+
+		if (!llist_empty(&queue->msg_queue))
+			fd->when |= BSC_FD_WRITE;
+	}
+
+	return 0;
+}
+
 /* callback when there's something to read from the l1 msg_queue */
 static int l1if_fd_cb(struct osmo_fd *ofd, unsigned int what)
 {
@@ -185,6 +253,7 @@ int l1if_transport_open(int q, struct femtol1_hdl *hdl)
 	}
 	osmo_wqueue_init(wq, 10);
 	wq->write_cb = l1fd_write_cb;
+	write_ofd->cb = wqueue_vector_cb;
 	write_ofd->fd = rc;
 	write_ofd->priv_nr = q;
 	write_ofd->data = hdl;