ipcpd: Add congestion avoidance policies

This adds congestion avoidance policies to the unicast IPCP.  The
default policy is a multi-bit explicit congestion avoidance algorithm
based on data-center TCP congestion avoidance (DCTCP) to relay
information about the maximum queue depth that packets experienced to
the receiver. There's also a "nop" policy to disable congestion
avoidance for testing and benchmarking purposes.

The (initial) API for congestion avoidance policies is:

        void *   (* ctx_create)(void);

        void     (* ctx_destroy)(void * ctx);

These calls create / and or destroy a context for congestion control
for a specific flow. Thread-safety of the context is the
responsability of the flow allocator (operations on the ctx should be
performed under a lock).

        ca_wnd_t (* ctx_update_snd)(void * ctx,
                                    size_t len);

This is the sender call to update the context, and should be called
for every packet that is sent on the flow. The len parameter in this
API is the packet length, which allows calculating the bandwidth. It
returns an opaque union type that is used for the call to check/wait
if the congestion window is open or closed (and allowing to release
locks before waiting).

        bool     (* ctx_update_rcv)(void *     ctx,
                                    size_t     len,
                                    uint8_t    ecn,
                                    uint16_t * ece);

This is the call to update the flow congestion context on the receiver
side. It should be called for every received packet.  It gets the ecn
value from the packet and its length, and returns the ECE (explicit
congestion experienced) value to be sent to the sender in case of
congestion. The boolean returned signals whether or not a congestion
update needs to be sent.

        void     (* ctx_update_ece)(void *   ctx,
                                    uint16_t ece);

This is the call for the sending side top update the context when it
receives an ECE update from the receiver.

        void     (* wnd_wait)(ca_wnd_t wnd);

This is a (blocking) call that waits for the congestion window to
clear. It should be stateless (to avoid waiting under locks). This may
change later on if passing the context is needed for different algorithms.

        uint8_t  (* calc_ecn)(int    fd,
                              size_t len);

This is the call that intermediate IPCPs(routers) should use to update
the ECN field on passing packets.

The multi-bit ECN policy bases the value for the ECN field on the
depth of the rbuff queue packets will be sent on. I created another
call to grab the queue depth as fccntl is write-locking the
application. We can further optimize this to avoid most locking on the
rbuff.

Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>

1 files changed, 61 insertions, 0 deletions

diff --git a/src/ipcpd/unicast/ca.h b/src/ipcpd/unicast/ca.h
new file mode 100644
index 00000000..5cf6199c
--- /dev/null
+++ b/src/ipcpd/unicast/ca.h
@@ -0,0 +1,61 @@
+/*
+ * Ouroboros - Copyright (C) 2016 - 2020
+ *
+ * Congestion avoidance
+ *
+ *    Dimitri Staessens <[email protected]>
+ *    Sander Vrijders   <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., http://www.fsf.org/about/contact/.
+ */
+
+#ifndef OUROBOROS_IPCPD_UNICAST_CA_H
+#define OUROBOROS_IPCPD_UNICAST_CA_H
+
+#include <ouroboros/ipcp.h>
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+typedef union {
+        time_t wait;
+} ca_wnd_t;
+
+int      ca_init(enum pol_cong_avoid ca);
+
+void     ca_fini(void);
+
+
+/* OPS */
+void *   ca_ctx_create(void);
+
+void     ca_ctx_destroy(void * ctx);
+
+ca_wnd_t ca_ctx_update_snd(void * ctx,
+                           size_t len);
+
+bool     ca_ctx_update_rcv(void *     ctx,
+                           size_t     len,
+                           uint8_t    ecn,
+                           uint16_t * ece);
+
+void     ca_ctx_update_ece(void *   ctx,
+                           uint16_t ece);
+
+void     ca_wnd_wait(ca_wnd_t wnd);
+
+uint8_t  ca_calc_ecn(int    fd,
+                     size_t len);
+
+#endif /* OUROBOROS_IPCPD_UNICAST_CA_H */