sctp: add fair capacity stream scheduler

As it says in rfc8260#section-3.5 about the fair capacity scheduler:

   A fair capacity distribution between the streams is used.  This
   scheduler considers the lengths of the messages of each stream and
   schedules them in a specific way to maintain an equal capacity for
   all streams.  The details are implementation dependent.  interleaving
   user messages allows for a better realization of the fair capacity
   usage.

This patch adds Fair Capacity Scheduler based on the foundations added
by commit 5bbbbe32a431 ("sctp: introduce stream scheduler foundations"):

A fc_list and a fc_length are added into struct sctp_stream_out_ext and
a fc_list is added into struct sctp_stream. In .enqueue, when there are
chunks enqueued into a stream, this stream will be linked into stream->
fc_list by its fc_list ordered by its fc_length. In .dequeue, it always
picks up the 1st skb from stream->fc_list. In .dequeue_done, fc_length
is increased by chunk's len and update its location in stream->fc_list
according to the its new fc_length.

Note that when the new fc_length overflows in .dequeue_done, instead of
resetting all fc_lengths to 0, we only reduced them by U32_MAX / 4 to
avoid a moment of imbalance in the scheduling, as Marcelo suggested.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/net/sctp/stream_sched.h b/include/net/sctp/stream_sched.h
index fa00dc2..9131707 100644 (file)
--- a/include/net/sctp/stream_sched.h
+++ b/include/net/sctp/stream_sched.h
@@ -58,5 +58,6 @@ void sctp_sched_ops_register(enum sctp_sched_type sched,
                             struct sctp_sched_ops *sched_ops);
 void sctp_sched_ops_prio_init(void);
 void sctp_sched_ops_rr_init(void);
+void sctp_sched_ops_fc_init(void);
 
 #endif /* __sctp_stream_sched_h__ */

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index e1f6e7f..2f1c9f5 100644 (file)
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1429,6 +1429,10 @@ struct sctp_stream_out_ext {
                struct {
                        struct list_head rr_list;
                };
+               struct {
+                       struct list_head fc_list;
+                       __u32 fc_length;
+               };
        };
 };
 
@@ -1475,6 +1479,9 @@ struct sctp_stream {
                        /* The next stream in line */
                        struct sctp_stream_out_ext *rr_next;
                };
+               struct {
+                       struct list_head fc_list;
+               };
        };
        struct sctp_stream_interleave *si;
 };

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index ed7d4ec..6814c5a 100644 (file)
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -1211,7 +1211,8 @@ enum sctp_sched_type {
        SCTP_SS_DEFAULT = SCTP_SS_FCFS,
        SCTP_SS_PRIO,
        SCTP_SS_RR,
-       SCTP_SS_MAX = SCTP_SS_RR
+       SCTP_SS_FC,
+       SCTP_SS_MAX = SCTP_SS_FC
 };
 
 /* Probe Interval socket option */

diff --git a/net/sctp/Makefile b/net/sctp/Makefile
index e845e45..0448398 100644 (file)
--- a/net/sctp/Makefile
+++ b/net/sctp/Makefile
@@ -13,7 +13,8 @@ sctp-y := sm_statetable.o sm_statefuns.o sm_sideeffect.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 \
-         stream_sched_rr.o stream_interleave.o
+         stream_sched_rr.o stream_sched_fc.o \
+         stream_interleave.o
 
 sctp_diag-y := diag.o
 

diff --git a/net/sctp/stream_sched.c b/net/sctp/stream_sched.c
index 3300670..1ebd14e 100644 (file)
--- a/net/sctp/stream_sched.c
+++ b/net/sctp/stream_sched.c
@@ -124,6 +124,7 @@ void sctp_sched_ops_init(void)
        sctp_sched_ops_fcfs_init();
        sctp_sched_ops_prio_init();
        sctp_sched_ops_rr_init();
+       sctp_sched_ops_fc_init();
 }
 
 static void sctp_sched_free_sched(struct sctp_stream *stream)

diff --git a/net/sctp/stream_sched_fc.c b/net/sctp/stream_sched_fc.c
new file mode 100644 (file)
index 0000000..b336c2f
--- /dev/null
+++ b/net/sctp/stream_sched_fc.c
@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* SCTP kernel implementation
+ * (C) Copyright Red Hat Inc. 2022
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * These functions manipulate sctp stream queue/scheduling.
+ *
+ * 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:
+ *    Xin Long <lucien.xin@gmail.com>
+ */
+
+#include <linux/list.h>
+#include <net/sctp/sctp.h>
+#include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
+
+/* Fair Capacity handling
+ * RFC 8260 section 3.5
+ */
+static void sctp_sched_fc_unsched_all(struct sctp_stream *stream);
+
+static int sctp_sched_fc_set(struct sctp_stream *stream, __u16 sid,
+                            __u16 weight, gfp_t gfp)
+{
+       return 0;
+}
+
+static int sctp_sched_fc_get(struct sctp_stream *stream, __u16 sid,
+                            __u16 *value)
+{
+       return 0;
+}
+
+static int sctp_sched_fc_init(struct sctp_stream *stream)
+{
+       INIT_LIST_HEAD(&stream->fc_list);
+
+       return 0;
+}
+
+static int sctp_sched_fc_init_sid(struct sctp_stream *stream, __u16 sid,
+                                 gfp_t gfp)
+{
+       struct sctp_stream_out_ext *soute = SCTP_SO(stream, sid)->ext;
+
+       INIT_LIST_HEAD(&soute->fc_list);
+       soute->fc_length = 0;
+
+       return 0;
+}
+
+static void sctp_sched_fc_free_sid(struct sctp_stream *stream, __u16 sid)
+{
+}
+
+static void sctp_sched_fc_sched(struct sctp_stream *stream,
+                               struct sctp_stream_out_ext *soute)
+{
+       struct sctp_stream_out_ext *pos;
+
+       if (!list_empty(&soute->fc_list))
+               return;
+
+       list_for_each_entry(pos, &stream->fc_list, fc_list)
+               if (pos->fc_length >= soute->fc_length)
+                       break;
+       list_add_tail(&soute->fc_list, &pos->fc_list);
+}
+
+static void sctp_sched_fc_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_fc_sched(stream, SCTP_SO(stream, sid)->ext);
+}
+
+static struct sctp_chunk *sctp_sched_fc_dequeue(struct sctp_outq *q)
+{
+       struct sctp_stream *stream = &q->asoc->stream;
+       struct sctp_stream_out_ext *soute;
+       struct sctp_chunk *ch;
+
+       /* Bail out quickly if queue is empty */
+       if (list_empty(&q->out_chunk_list))
+               return NULL;
+
+       /* Find which chunk is next */
+       if (stream->out_curr)
+               soute = stream->out_curr->ext;
+       else
+               soute = list_entry(stream->fc_list.next, struct sctp_stream_out_ext, fc_list);
+       ch = list_entry(soute->outq.next, struct sctp_chunk, stream_list);
+
+       sctp_sched_dequeue_common(q, ch);
+       return ch;
+}
+
+static void sctp_sched_fc_dequeue_done(struct sctp_outq *q,
+                                      struct sctp_chunk *ch)
+{
+       struct sctp_stream *stream = &q->asoc->stream;
+       struct sctp_stream_out_ext *soute, *pos;
+       __u16 sid, i;
+
+       sid = sctp_chunk_stream_no(ch);
+       soute = SCTP_SO(stream, sid)->ext;
+       /* reduce all fc_lengths by U32_MAX / 4 if the current fc_length overflows. */
+       if (soute->fc_length > U32_MAX - ch->skb->len) {
+               for (i = 0; i < stream->outcnt; i++) {
+                       pos = SCTP_SO(stream, i)->ext;
+                       if (!pos)
+                               continue;
+                       if (pos->fc_length <= (U32_MAX >> 2)) {
+                               pos->fc_length = 0;
+                               continue;
+                       }
+                       pos->fc_length -= (U32_MAX >> 2);
+               }
+       }
+       soute->fc_length += ch->skb->len;
+
+       if (list_empty(&soute->outq)) {
+               list_del_init(&soute->fc_list);
+               return;
+       }
+
+       pos = soute;
+       list_for_each_entry_continue(pos, &stream->fc_list, fc_list)
+               if (pos->fc_length >= soute->fc_length)
+                       break;
+       list_move_tail(&soute->fc_list, &pos->fc_list);
+}
+
+static void sctp_sched_fc_sched_all(struct sctp_stream *stream)
+{
+       struct sctp_association *asoc;
+       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 = sctp_chunk_stream_no(ch);
+
+               if (SCTP_SO(stream, sid)->ext)
+                       sctp_sched_fc_sched(stream, SCTP_SO(stream, sid)->ext);
+       }
+}
+
+static void sctp_sched_fc_unsched_all(struct sctp_stream *stream)
+{
+       struct sctp_stream_out_ext *soute, *tmp;
+
+       list_for_each_entry_safe(soute, tmp, &stream->fc_list, fc_list)
+               list_del_init(&soute->fc_list);
+}
+
+static struct sctp_sched_ops sctp_sched_fc = {
+       .set = sctp_sched_fc_set,
+       .get = sctp_sched_fc_get,
+       .init = sctp_sched_fc_init,
+       .init_sid = sctp_sched_fc_init_sid,
+       .free_sid = sctp_sched_fc_free_sid,
+       .enqueue = sctp_sched_fc_enqueue,
+       .dequeue = sctp_sched_fc_dequeue,
+       .dequeue_done = sctp_sched_fc_dequeue_done,
+       .sched_all = sctp_sched_fc_sched_all,
+       .unsched_all = sctp_sched_fc_unsched_all,
+};
+
+void sctp_sched_ops_fc_init(void)
+{
+       sctp_sched_ops_register(SCTP_SS_FC, &sctp_sched_fc);
+}