llc: Add CoDel AQM implementation
This commit adds an implementation of the CoDel algorithm based on
the reference pseudocode presented in
http://queue.acm.org/appendices/codel.html. Instead of abstracting
the queue itself, the implementation provides a time stamp based
automaton which is invoked after a package has been dequeued.
Note that the modifications of the algorithm shown in
https://tools.ietf.org/html/draft-ietf-aqm-codel-01 are not yet
applied.
Sponsored-by: On-Waves ehf
diff --git a/src/gprs_codel.c b/src/gprs_codel.c
new file mode 100644
index 0000000..02440b4
--- /dev/null
+++ b/src/gprs_codel.c
@@ -0,0 +1,179 @@
+/* gprs_codel.cpp
+ *
+ * Copyright (C) 2015 by Sysmocom s.f.m.c. GmbH
+ * Author: Jacob Erlbeck <jerlbeck@sysmocom.de>
+ *
+ * This program 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
+ * of the License, or (at your option) any later version.
+ *
+ * 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#include "gprs_codel.h"
+#include "gprs_debug.h"
+
+#include <osmocom/core/utils.h>
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <math.h>
+
+static void control_law(struct gprs_codel *state, struct timeval *delta)
+{
+ /* 256 / sqrt(x), limited to 255 */
+ static uint8_t inv_sqrt_tab[] = {255,
+ 255, 181, 147, 128, 114, 104, 96, 90, 85, 80, 77, 73, 71, 68,
+ 66, 64, 62, 60, 58, 57, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46,
+ 45, 45, 44, 43, 43, 42, 42, 41, 40, 40, 39, 39, 39, 38, 38, 37,
+ 37, 36, 36, 36, 35, 35, 35, 34, 34, 34, 33, 33, 33, 33, 32, 32,
+ 32, 32, 31, 31, 31, 31, 30, 30, 30, 30, 29, 29, 29, 29, 29, 28,
+ 28, 28, 28, 28, 28, 27, 27, 27, 27, 27, 27, 26, 26, 26, 26, 26,
+ 26, 26, 25, 25, 25, 25, 25, 25, 25, 25, 24, 24, 24, 24, 24, 24,
+ 24, 24, 24, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 22, 22, 22,
+ 22, 22, 22, 22, 22, 22, 22, 22, 22, 21, 21, 21, 21, 21, 21, 21,
+ 21, 21, 21, 21, 21, 21, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
+ 20, 20, 20, 20, 20, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19,
+ 19, 19, 19, 19, 19, 19, 19, 18, 18, 18, 18, 18, 18, 18, 18, 18,
+ 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 17, 17, 17, 17,
+ 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17,
+ 17, 17, 17, 17
+ };
+ uint_fast32_t delta_usecs;
+ uint_fast32_t inv_sqrt;
+ div_t q;
+
+ if (state->count >= ARRAY_SIZE(inv_sqrt_tab))
+ inv_sqrt = 16;
+ else
+ inv_sqrt = inv_sqrt_tab[state->count];
+
+ /* delta = state->interval / sqrt(count) */
+ delta_usecs = state->interval.tv_sec * 1000000 + state->interval.tv_usec;
+ delta_usecs = delta_usecs * inv_sqrt / 256;
+
+ q = div(delta_usecs, 1000000);
+ delta->tv_sec = q.quot;
+ delta->tv_usec = q.rem;
+}
+
+void gprs_codel_init(struct gprs_codel *state)
+{
+ static const struct gprs_codel init_state = {0};
+
+ *state = init_state;
+ gprs_codel_set_interval(state, -1);
+ gprs_codel_set_maxpacket(state, -1);
+}
+
+void gprs_codel_set_interval(struct gprs_codel *state, int interval_ms)
+{
+ div_t q;
+
+ if (interval_ms <= 0)
+ interval_ms = GPRS_CODEL_DEFAULT_INTERVAL_MS;
+
+ q = div(interval_ms, 1000);
+ state->interval.tv_sec = q.quot;
+ state->interval.tv_usec = q.rem * 1000;
+
+ /* target ~ 5% of interval */
+ q = div(interval_ms * 13 / 256, 1000);
+ state->target.tv_sec = q.quot;
+ state->target.tv_usec = q.rem * 1000;
+}
+
+void gprs_codel_set_maxpacket(struct gprs_codel *state, int maxpacket)
+{
+
+ if (maxpacket < 0)
+ maxpacket = GPRS_CODEL_DEFAULT_MAXPACKET;
+
+ state->maxpacket = maxpacket;
+}
+
+/*
+ * This is an broken up variant of the algorithm being described in
+ * http://queue.acm.org/appendices/codel.html
+ */
+int gprs_codel_control(struct gprs_codel *state, const struct timeval *recv,
+ const struct timeval *now, int bytes)
+{
+ struct timeval sojourn_time;
+ struct timeval delta;
+
+ if (recv == NULL)
+ goto stop_dropping;
+
+ timersub(now, recv, &sojourn_time);
+
+ if (timercmp(&sojourn_time, &state->target, <))
+ goto stop_dropping;
+
+ if (bytes >= 0 && (unsigned)bytes <= state->maxpacket)
+ goto stop_dropping;
+
+ if (!timerisset(&state->first_above_time)) {
+ timeradd(now, &state->interval, &state->first_above_time);
+ goto not_ok_to_drop;
+ }
+
+ if (timercmp(now, &state->first_above_time, <))
+ goto not_ok_to_drop;
+
+ /* Ok to drop */
+
+ if (!state->dropping) {
+ int recently = 0;
+ int in_drop_cycle = 0;
+ if (timerisset(&state->drop_next)) {
+ timersub(now, &state->drop_next, &delta);
+ in_drop_cycle = timercmp(&delta, &state->interval, <);
+ recently = in_drop_cycle;
+ }
+ if (!recently) {
+ timersub(now, &state->first_above_time, &delta);
+ recently = !timercmp(&delta, &state->interval, <);
+ };
+ if (!recently)
+ return 0;
+
+ state->dropping = 1;
+
+ if (in_drop_cycle && state->count > 2)
+ state->count -= 2;
+ else
+ state->count = 1;
+
+ state->drop_next = *now;
+ } else {
+ if (timercmp(now, &state->drop_next, <))
+ return 0;
+
+ state->count += 1;
+ }
+
+ control_law(state, &delta);
+ timeradd(&state->drop_next, &delta, &state->drop_next);
+
+#if 1
+ LOGP(DRLCMAC, LOGL_INFO,
+ "CoDel decided to drop packet, window = %d.%03dms, count = %d\n",
+ (int)delta.tv_sec, (int)(delta.tv_usec / 1000), state->count);
+#endif
+ return 1;
+
+stop_dropping:
+ timerclear(&state->first_above_time);
+not_ok_to_drop:
+ state->dropping = 0;
+ return 0;
+}