sctp: introduce round robin stream scheduler

This patch introduces RFC Draft ndata section 3.2 Priority Based
Scheduler (SCTP_SS_RR).

Works by maintaining a list of enqueued streams and tracking the last
one used to send data. When the datamsg is done, it switches to the next
stream.

See-also: https://tools.ietf.org/html/draft-ietf-tsvwg-sctp-ndata-13


Tested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -1348,6 +1348,10 @@ struct sctp_stream_out_ext {
 			struct list_head prio_list;
 			struct sctp_stream_priorities *prio_head;
 		};
+		/* Fields used by RR scheduler */
+		struct {
+			struct list_head rr_list;
+		};
 	};
 };
 
@@ -1374,6 +1378,13 @@ struct sctp_stream {
 			/* List of priorities scheduled */
 			struct list_head prio_list;
 		};
+		/* Fields used by RR scheduler */
+		struct {
+			/* List of streams scheduled */
+			struct list_head rr_list;
+			/* The next stream stream in line */
+			struct sctp_stream_out_ext *rr_next;
+		};
 	};
 };
 

include/uapi/linux/sctp.h

@@ -1100,7 +1100,8 @@ struct sctp_add_streams {
 enum sctp_sched_type {
 	SCTP_SS_FCFS,
 	SCTP_SS_PRIO,
-	SCTP_SS_MAX = SCTP_SS_PRIO
+	SCTP_SS_RR,
+	SCTP_SS_MAX = SCTP_SS_RR
 };
 
 #endif /* _UAPI_SCTP_H */

net/sctp/Makefile

@@ -12,7 +12,8 @@ sctp-y := sm_statetable.o sm_statefuns.o sm_sideeffect.o \
 	  inqueue.o outqueue.o ulpqueue.o \
 	  tsnmap.o bind_addr.o socket.o primitive.o \
 	  output.o input.o debug.o stream.o auth.o \
-	  offload.o stream_sched.o stream_sched_prio.o
+	  offload.o stream_sched.o stream_sched_prio.o \
+	  stream_sched_rr.o
 
 sctp_probe-y := probe.o
 

net/sctp/stream_sched.c

@@ -122,10 +122,12 @@ static struct sctp_sched_ops sctp_sched_fcfs = {
 /* API to other parts of the stack */
 
 extern struct sctp_sched_ops sctp_sched_prio;
+extern struct sctp_sched_ops sctp_sched_rr;
 
 struct sctp_sched_ops *sctp_sched_ops[] = {
 	&sctp_sched_fcfs,
 	&sctp_sched_prio,
+	&sctp_sched_rr,
 };
 
 int sctp_sched_set_sched(struct sctp_association *asoc,

net/sctp/stream_sched_rr.c

+/* SCTP kernel implementation
+ * (C) Copyright Red Hat Inc. 2017
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * These functions manipulate sctp stream queue/scheduling.
+ *
+ * This SCTP implementation is free software;
+ * you can redistribute it and/or modify it under the terms of
+ * the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This SCTP implementation is distributed in the hope that it
+ * will be useful, but WITHOUT ANY WARRANTY; without even the implied
+ *                 ************************
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU CC; see the file COPYING.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * Please send any bug reports or fixes you make to the
+ * email addresched(es):
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *    Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
+ */
+
+#include <linux/list.h>
+#include <net/sctp/sctp.h>
+#include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
+
+/* Priority handling
+ * RFC DRAFT ndata section 3.2
+ */
+static void sctp_sched_rr_unsched_all(struct sctp_stream *stream);
+
+static void sctp_sched_rr_next_stream(struct sctp_stream *stream)
+{
+	struct list_head *pos;
+
+	pos = stream->rr_next->rr_list.next;
+	if (pos == &stream->rr_list)
+		pos = pos->next;
+	stream->rr_next = list_entry(pos, struct sctp_stream_out_ext, rr_list);
+}
+
+static void sctp_sched_rr_unsched(struct sctp_stream *stream,
+				  struct sctp_stream_out_ext *soute)
+{
+	if (stream->rr_next == soute)
+		/* Try to move to the next stream */
+		sctp_sched_rr_next_stream(stream);
+
+	list_del_init(&soute->rr_list);
+
+	/* If we have no other stream queued, clear next */
+	if (list_empty(&stream->rr_list))
+		stream->rr_next = NULL;
+}
+
+static void sctp_sched_rr_sched(struct sctp_stream *stream,
+				struct sctp_stream_out_ext *soute)
+{
+	if (!list_empty(&soute->rr_list))
+		/* Already scheduled. */
+		return;
+
+	/* Schedule the stream */
+	list_add_tail(&soute->rr_list, &stream->rr_list);
+
+	if (!stream->rr_next)
+		stream->rr_next = soute;
+}
+
+static int sctp_sched_rr_set(struct sctp_stream *stream, __u16 sid,
+			     __u16 prio, gfp_t gfp)
+{
+	return 0;
+}
+
+static int sctp_sched_rr_get(struct sctp_stream *stream, __u16 sid,
+			     __u16 *value)
+{
+	return 0;
+}
+
+static int sctp_sched_rr_init(struct sctp_stream *stream)
+{
+	INIT_LIST_HEAD(&stream->rr_list);
+	stream->rr_next = NULL;
+
+	return 0;
+}
+
+static int sctp_sched_rr_init_sid(struct sctp_stream *stream, __u16 sid,
+				  gfp_t gfp)
+{
+	INIT_LIST_HEAD(&stream->out[sid].ext->rr_list);
+
+	return 0;
+}
+
+static void sctp_sched_rr_free(struct sctp_stream *stream)
+{
+	sctp_sched_rr_unsched_all(stream);
+}
+
+static void sctp_sched_rr_enqueue(struct sctp_outq *q,
+				  struct sctp_datamsg *msg)
+{
+	struct sctp_stream *stream;
+	struct sctp_chunk *ch;
+	__u16 sid;
+
+	ch = list_first_entry(&msg->chunks, struct sctp_chunk, frag_list);
+	sid = sctp_chunk_stream_no(ch);
+	stream = &q->asoc->stream;
+	sctp_sched_rr_sched(stream, stream->out[sid].ext);
+}
+
+static struct sctp_chunk *sctp_sched_rr_dequeue(struct sctp_outq *q)
+{
+	struct sctp_stream *stream = &q->asoc->stream;
+	struct sctp_stream_out_ext *soute;
+	struct sctp_chunk *ch = NULL;
+
+	/* Bail out quickly if queue is empty */
+	if (list_empty(&q->out_chunk_list))
+		goto out;
+
+	/* Find which chunk is next */
+	if (stream->out_curr)
+		soute = stream->out_curr->ext;
+	else
+		soute = stream->rr_next;
+	ch = list_entry(soute->outq.next, struct sctp_chunk, stream_list);
+
+	sctp_sched_dequeue_common(q, ch);
+
+out:
+	return ch;
+}
+
+static void sctp_sched_rr_dequeue_done(struct sctp_outq *q,
+				       struct sctp_chunk *ch)
+{
+	struct sctp_stream_out_ext *soute;
+	__u16 sid;
+
+	/* Last chunk on that msg, move to the next stream */
+	sid = sctp_chunk_stream_no(ch);
+	soute = q->asoc->stream.out[sid].ext;
+
+	sctp_sched_rr_next_stream(&q->asoc->stream);
+
+	if (list_empty(&soute->outq))
+		sctp_sched_rr_unsched(&q->asoc->stream, soute);
+}
+
+static void sctp_sched_rr_sched_all(struct sctp_stream *stream)
+{
+	struct sctp_association *asoc;
+	struct sctp_stream_out_ext *soute;
+	struct sctp_chunk *ch;
+
+	asoc = container_of(stream, struct sctp_association, stream);
+	list_for_each_entry(ch, &asoc->outqueue.out_chunk_list, list) {
+		__u16 sid;
+
+		sid = sctp_chunk_stream_no(ch);
+		soute = stream->out[sid].ext;
+		if (soute)
+			sctp_sched_rr_sched(stream, soute);
+	}
+}
+
+static void sctp_sched_rr_unsched_all(struct sctp_stream *stream)
+{
+	struct sctp_stream_out_ext *soute, *tmp;
+
+	list_for_each_entry_safe(soute, tmp, &stream->rr_list, rr_list)
+		sctp_sched_rr_unsched(stream, soute);
+}
+
+struct sctp_sched_ops sctp_sched_rr = {
+	.set = sctp_sched_rr_set,
+	.get = sctp_sched_rr_get,
+	.init = sctp_sched_rr_init,
+	.init_sid = sctp_sched_rr_init_sid,
+	.free = sctp_sched_rr_free,
+	.enqueue = sctp_sched_rr_enqueue,
+	.dequeue = sctp_sched_rr_dequeue,
+	.dequeue_done = sctp_sched_rr_dequeue_done,
+	.sched_all = sctp_sched_rr_sched_all,
+	.unsched_all = sctp_sched_rr_unsched_all,
+};