[PATCH 0/2] codel: make it reuseable beyond qdiscs

[PATCH 0/2] codel: make it reuseable beyond qdiscs

[Michal Kazior]

Hi,

There's an ongoing effort in fixing wireless
bufferbloat. As part of that fq_codel is being
ported into mac80211. To prevent code duplication
codel.h needs to be slightly modified before it
can be used in mac80211 (or other drivers FWIW).

For more background please see:

  https://www.spinics.net/lists/linux-wireless/msg149976.html


Michal Kazior (2):
  codel: generalize the implementation
  codel: split into multiple files

 include/net/codel.h       | 217 +--------------------------------------
 include/net/codel_impl.h  | 255 ++++++++++++++++++++++++++++++++++++++++++++++
 include/net/codel_qdisc.h |  73 +++++++++++++
 net/sched/sch_codel.c     |  22 +++-
 net/sched/sch_fq_codel.c  |  21 +++-
 5 files changed, 368 insertions(+), 220 deletions(-)
 create mode 100644 include/net/codel_impl.h
 create mode 100644 include/net/codel_qdisc.h

-- 
2.1.4

[PATCH 1/2] codel: generalize the implementation

[Michal Kazior]

This strips out qdisc specific bits from the code
and makes it slightly more reusable. Codel will be
used by wireless/mac80211 in the future.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
---
 include/net/codel.h      | 64 +++++++++++++++++++++++++++++-------------------
 net/sched/sch_codel.c    | 20 ++++++++++++---
 net/sched/sch_fq_codel.c | 19 +++++++++++---
 3 files changed, 71 insertions(+), 32 deletions(-)

diff --git a/include/net/codel.h b/include/net/codel.h
index d168aca115cc..06ac687b4909 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -176,12 +176,10 @@ struct codel_stats {
 
 #define CODEL_DISABLED_THRESHOLD INT_MAX
 
-static void codel_params_init(struct codel_params *params,
-			      const struct Qdisc *sch)
+static void codel_params_init(struct codel_params *params)
 {
 	params->interval = MS2TIME(100);
 	params->target = MS2TIME(5);
-	params->mtu = psched_mtu(qdisc_dev(sch));
 	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
 	params->ecn = false;
 }
@@ -226,28 +224,38 @@ static codel_time_t codel_control_law(codel_time_t t,
 	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
 }
 
+typedef u32 (*codel_skb_len_t)(const struct sk_buff *skb);
+typedef codel_time_t (*codel_skb_time_t)(const struct sk_buff *skb);
+typedef void (*codel_skb_drop_t)(struct sk_buff *skb, void *ctx);
+typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
+						void *ctx);
+
 static bool codel_should_drop(const struct sk_buff *skb,
-			      struct Qdisc *sch,
+			      void *ctx,
 			      struct codel_vars *vars,
 			      struct codel_params *params,
 			      struct codel_stats *stats,
+			      codel_skb_len_t skb_len_func,
+			      codel_skb_time_t skb_time_func,
+			      u32 *backlog,
 			      codel_time_t now)
 {
 	bool ok_to_drop;
+	u32 skb_len;
 
 	if (!skb) {
 		vars->first_above_time = 0;
 		return false;
 	}
 
-	vars->ldelay = now - codel_get_enqueue_time(skb);
-	sch->qstats.backlog -= qdisc_pkt_len(skb);
+	skb_len = skb_len_func(skb);
+	vars->ldelay = now - skb_time_func(skb);
 
-	if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
-		stats->maxpacket = qdisc_pkt_len(skb);
+	if (unlikely(skb_len > stats->maxpacket))
+		stats->maxpacket = skb_len;
 
 	if (codel_time_before(vars->ldelay, params->target) ||
-	    sch->qstats.backlog <= params->mtu) {
+	    *backlog <= params->mtu) {
 		/* went below - stay below for at least interval */
 		vars->first_above_time = 0;
 		return false;
@@ -264,16 +272,17 @@ static bool codel_should_drop(const struct sk_buff *skb,
 	return ok_to_drop;
 }
 
-typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
-						struct Qdisc *sch);
-
-static struct sk_buff *codel_dequeue(struct Qdisc *sch,
+static struct sk_buff *codel_dequeue(void *ctx,
+				     u32 *backlog,
 				     struct codel_params *params,
 				     struct codel_vars *vars,
 				     struct codel_stats *stats,
+				     codel_skb_len_t skb_len_func,
+				     codel_skb_time_t skb_time_func,
+				     codel_skb_drop_t drop_func,
 				     codel_skb_dequeue_t dequeue_func)
 {
-	struct sk_buff *skb = dequeue_func(vars, sch);
+	struct sk_buff *skb = dequeue_func(vars, ctx);
 	codel_time_t now;
 	bool drop;
 
@@ -282,7 +291,8 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 		return skb;
 	}
 	now = codel_get_time();
-	drop = codel_should_drop(skb, sch, vars, params, stats, now);
+	drop = codel_should_drop(skb, ctx, vars, params, stats,
+				 skb_len_func, skb_time_func, backlog, now);
 	if (vars->dropping) {
 		if (!drop) {
 			/* sojourn time below target - leave dropping state */
@@ -310,12 +320,15 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 								  vars->rec_inv_sqrt);
 					goto end;
 				}
-				stats->drop_len += qdisc_pkt_len(skb);
-				qdisc_drop(skb, sch);
+				stats->drop_len += skb_len_func(skb);
+				drop_func(skb, ctx);
 				stats->drop_count++;
-				skb = dequeue_func(vars, sch);
-				if (!codel_should_drop(skb, sch,
-						       vars, params, stats, now)) {
+				skb = dequeue_func(vars, ctx);
+				if (!codel_should_drop(skb, ctx,
+						       vars, params, stats,
+						       skb_len_func,
+						       skb_time_func,
+						       backlog, now)) {
 					/* leave dropping state */
 					vars->dropping = false;
 				} else {
@@ -333,13 +346,14 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 		if (params->ecn && INET_ECN_set_ce(skb)) {
 			stats->ecn_mark++;
 		} else {
-			stats->drop_len += qdisc_pkt_len(skb);
-			qdisc_drop(skb, sch);
+			stats->drop_len += skb_len_func(skb);
+			drop_func(skb, ctx);
 			stats->drop_count++;
 
-			skb = dequeue_func(vars, sch);
-			drop = codel_should_drop(skb, sch, vars, params,
-						 stats, now);
+			skb = dequeue_func(vars, ctx);
+			drop = codel_should_drop(skb, ctx, vars, params,
+						 stats, skb_len_func,
+						 skb_time_func, backlog, now);
 		}
 		vars->dropping = true;
 		/* if min went above target close to when we last went below it
diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index 9b7e2980ee5c..512a94abe351 100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -64,20 +64,33 @@ struct codel_sched_data {
  * to dequeue a packet from queue. Note: backlog is handled in
  * codel, we dont need to reduce it here.
  */
-static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
+static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)
 {
+	struct Qdisc *sch = ctx;
 	struct sk_buff *skb = __skb_dequeue(&sch->q);
 
+	if (skb)
+		sch->qstats.backlog -= qdisc_pkt_len(skb);
+
 	prefetch(&skb->end); /* we'll need skb_shinfo() */
 	return skb;
 }
 
+static void drop_func(struct sk_buff *skb, void *ctx)
+{
+	struct Qdisc *sch = ctx;
+
+	qdisc_drop(skb, sch);
+}
+
 static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
 {
 	struct codel_sched_data *q = qdisc_priv(sch);
 	struct sk_buff *skb;
 
-	skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats, dequeue);
+	skb = codel_dequeue(sch, &sch->qstats.backlog, &q->params, &q->vars,
+			    &q->stats, qdisc_pkt_len, codel_get_enqueue_time,
+			    drop_func, dequeue_func);
 
 	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
 	 * or HTB crashes. Defer it for next round.
@@ -173,9 +186,10 @@ static int codel_init(struct Qdisc *sch, struct nlattr *opt)
 
 	sch->limit = DEFAULT_CODEL_LIMIT;
 
-	codel_params_init(&q->params, sch);
+	codel_params_init(&q->params);
 	codel_vars_init(&q->vars);
 	codel_stats_init(&q->stats);
+	q->params.mtu = psched_mtu(qdisc_dev(sch));
 
 	if (opt) {
 		int err = codel_change(sch, opt);
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index d3fc8f9dd3d4..dcf7266e6901 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -220,8 +220,9 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
  * to dequeue a packet from queue. Note: backlog is handled in
  * codel, we dont need to reduce it here.
  */
-static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
+static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)
 {
+	struct Qdisc *sch = ctx;
 	struct fq_codel_sched_data *q = qdisc_priv(sch);
 	struct fq_codel_flow *flow;
 	struct sk_buff *skb = NULL;
@@ -231,10 +232,18 @@ static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
 		skb = dequeue_head(flow);
 		q->backlogs[flow - q->flows] -= qdisc_pkt_len(skb);
 		sch->q.qlen--;
+		sch->qstats.backlog -= qdisc_pkt_len(skb);
 	}
 	return skb;
 }
 
+static void drop_func(struct sk_buff *skb, void *ctx)
+{
+	struct Qdisc *sch = ctx;
+
+	qdisc_drop(skb, sch);
+}
+
 static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
 {
 	struct fq_codel_sched_data *q = qdisc_priv(sch);
@@ -263,8 +272,9 @@ begin:
 	prev_ecn_mark = q->cstats.ecn_mark;
 	prev_backlog = sch->qstats.backlog;
 
-	skb = codel_dequeue(sch, &q->cparams, &flow->cvars, &q->cstats,
-			    dequeue);
+	skb = codel_dequeue(sch, &sch->qstats.backlog, &q->cparams,
+			    &flow->cvars, &q->cstats, qdisc_pkt_len,
+			    codel_get_enqueue_time, drop_func, dequeue_func);
 
 	flow->dropped += q->cstats.drop_count - prev_drop_count;
 	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
@@ -423,9 +433,10 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt)
 	q->perturbation = prandom_u32();
 	INIT_LIST_HEAD(&q->new_flows);
 	INIT_LIST_HEAD(&q->old_flows);
-	codel_params_init(&q->cparams, sch);
+	codel_params_init(&q->cparams);
 	codel_stats_init(&q->cstats);
 	q->cparams.ecn = true;
+	q->cparams.mtu = psched_mtu(qdisc_dev(sch));
 
 	if (opt) {
 		int err = fq_codel_change(sch, opt);
-- 
2.1.4

[PATCH 2/2] codel: split into multiple files

[Michal Kazior]

It was impossible to include codel.h for the
purpose of having access to codel_params or
codel_vars structure definitions and using them
for embedding in other more complex structures.

This splits allows codel.h itself to be treated
like any other header file while codel_qdisc.h and
codel_impl.h contain function definitions with
logic that was previously in codel.h.

This copies over copyrights and doesn't involve
code changes other than adding a few additional
include directives to net/sched/sch*codel.c.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
---
 include/net/codel.h       | 223 ----------------------------------------
 include/net/codel_impl.h  | 255 ++++++++++++++++++++++++++++++++++++++++++++++
 include/net/codel_qdisc.h |  73 +++++++++++++
 net/sched/sch_codel.c     |   2 +
 net/sched/sch_fq_codel.c  |   2 +
 5 files changed, 332 insertions(+), 223 deletions(-)
 create mode 100644 include/net/codel_impl.h
 create mode 100644 include/net/codel_qdisc.h

diff --git a/include/net/codel.h b/include/net/codel.h
index 06ac687b4909..a6e428f80135 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -87,27 +87,6 @@ static inline codel_time_t codel_get_time(void)
 	 ((s32)((a) - (b)) >= 0))
 #define codel_time_before_eq(a, b)	codel_time_after_eq(b, a)
 
-/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
-struct codel_skb_cb {
-	codel_time_t enqueue_time;
-};
-
-static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
-{
-	qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
-	return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
-}
-
-static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
-{
-	return get_codel_cb(skb)->enqueue_time;
-}
-
-static void codel_set_enqueue_time(struct sk_buff *skb)
-{
-	get_codel_cb(skb)->enqueue_time = codel_get_time();
-}
-
 static inline u32 codel_time_to_us(codel_time_t val)
 {
 	u64 valns = ((u64)val << CODEL_SHIFT);
@@ -176,212 +155,10 @@ struct codel_stats {
 
 #define CODEL_DISABLED_THRESHOLD INT_MAX
 
-static void codel_params_init(struct codel_params *params)
-{
-	params->interval = MS2TIME(100);
-	params->target = MS2TIME(5);
-	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
-	params->ecn = false;
-}
-
-static void codel_vars_init(struct codel_vars *vars)
-{
-	memset(vars, 0, sizeof(*vars));
-}
-
-static void codel_stats_init(struct codel_stats *stats)
-{
-	stats->maxpacket = 0;
-}
-
-/*
- * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
- * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
- *
- * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
- */
-static void codel_Newton_step(struct codel_vars *vars)
-{
-	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
-	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
-	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
-
-	val >>= 2; /* avoid overflow in following multiply */
-	val = (val * invsqrt) >> (32 - 2 + 1);
-
-	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
-}
-
-/*
- * CoDel control_law is t + interval/sqrt(count)
- * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
- * both sqrt() and divide operation.
- */
-static codel_time_t codel_control_law(codel_time_t t,
-				      codel_time_t interval,
-				      u32 rec_inv_sqrt)
-{
-	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
-}
-
 typedef u32 (*codel_skb_len_t)(const struct sk_buff *skb);
 typedef codel_time_t (*codel_skb_time_t)(const struct sk_buff *skb);
 typedef void (*codel_skb_drop_t)(struct sk_buff *skb, void *ctx);
 typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
 						void *ctx);
 
-static bool codel_should_drop(const struct sk_buff *skb,
-			      void *ctx,
-			      struct codel_vars *vars,
-			      struct codel_params *params,
-			      struct codel_stats *stats,
-			      codel_skb_len_t skb_len_func,
-			      codel_skb_time_t skb_time_func,
-			      u32 *backlog,
-			      codel_time_t now)
-{
-	bool ok_to_drop;
-	u32 skb_len;
-
-	if (!skb) {
-		vars->first_above_time = 0;
-		return false;
-	}
-
-	skb_len = skb_len_func(skb);
-	vars->ldelay = now - skb_time_func(skb);
-
-	if (unlikely(skb_len > stats->maxpacket))
-		stats->maxpacket = skb_len;
-
-	if (codel_time_before(vars->ldelay, params->target) ||
-	    *backlog <= params->mtu) {
-		/* went below - stay below for at least interval */
-		vars->first_above_time = 0;
-		return false;
-	}
-	ok_to_drop = false;
-	if (vars->first_above_time == 0) {
-		/* just went above from below. If we stay above
-		 * for at least interval we'll say it's ok to drop
-		 */
-		vars->first_above_time = now + params->interval;
-	} else if (codel_time_after(now, vars->first_above_time)) {
-		ok_to_drop = true;
-	}
-	return ok_to_drop;
-}
-
-static struct sk_buff *codel_dequeue(void *ctx,
-				     u32 *backlog,
-				     struct codel_params *params,
-				     struct codel_vars *vars,
-				     struct codel_stats *stats,
-				     codel_skb_len_t skb_len_func,
-				     codel_skb_time_t skb_time_func,
-				     codel_skb_drop_t drop_func,
-				     codel_skb_dequeue_t dequeue_func)
-{
-	struct sk_buff *skb = dequeue_func(vars, ctx);
-	codel_time_t now;
-	bool drop;
-
-	if (!skb) {
-		vars->dropping = false;
-		return skb;
-	}
-	now = codel_get_time();
-	drop = codel_should_drop(skb, ctx, vars, params, stats,
-				 skb_len_func, skb_time_func, backlog, now);
-	if (vars->dropping) {
-		if (!drop) {
-			/* sojourn time below target - leave dropping state */
-			vars->dropping = false;
-		} else if (codel_time_after_eq(now, vars->drop_next)) {
-			/* It's time for the next drop. Drop the current
-			 * packet and dequeue the next. The dequeue might
-			 * take us out of dropping state.
-			 * If not, schedule the next drop.
-			 * A large backlog might result in drop rates so high
-			 * that the next drop should happen now,
-			 * hence the while loop.
-			 */
-			while (vars->dropping &&
-			       codel_time_after_eq(now, vars->drop_next)) {
-				vars->count++; /* dont care of possible wrap
-						* since there is no more divide
-						*/
-				codel_Newton_step(vars);
-				if (params->ecn && INET_ECN_set_ce(skb)) {
-					stats->ecn_mark++;
-					vars->drop_next =
-						codel_control_law(vars->drop_next,
-								  params->interval,
-								  vars->rec_inv_sqrt);
-					goto end;
-				}
-				stats->drop_len += skb_len_func(skb);
-				drop_func(skb, ctx);
-				stats->drop_count++;
-				skb = dequeue_func(vars, ctx);
-				if (!codel_should_drop(skb, ctx,
-						       vars, params, stats,
-						       skb_len_func,
-						       skb_time_func,
-						       backlog, now)) {
-					/* leave dropping state */
-					vars->dropping = false;
-				} else {
-					/* and schedule the next drop */
-					vars->drop_next =
-						codel_control_law(vars->drop_next,
-								  params->interval,
-								  vars->rec_inv_sqrt);
-				}
-			}
-		}
-	} else if (drop) {
-		u32 delta;
-
-		if (params->ecn && INET_ECN_set_ce(skb)) {
-			stats->ecn_mark++;
-		} else {
-			stats->drop_len += skb_len_func(skb);
-			drop_func(skb, ctx);
-			stats->drop_count++;
-
-			skb = dequeue_func(vars, ctx);
-			drop = codel_should_drop(skb, ctx, vars, params,
-						 stats, skb_len_func,
-						 skb_time_func, backlog, now);
-		}
-		vars->dropping = true;
-		/* if min went above target close to when we last went below it
-		 * assume that the drop rate that controlled the queue on the
-		 * last cycle is a good starting point to control it now.
-		 */
-		delta = vars->count - vars->lastcount;
-		if (delta > 1 &&
-		    codel_time_before(now - vars->drop_next,
-				      16 * params->interval)) {
-			vars->count = delta;
-			/* we dont care if rec_inv_sqrt approximation
-			 * is not very precise :
-			 * Next Newton steps will correct it quadratically.
-			 */
-			codel_Newton_step(vars);
-		} else {
-			vars->count = 1;
-			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
-		}
-		vars->lastcount = vars->count;
-		vars->drop_next = codel_control_law(now, params->interval,
-						    vars->rec_inv_sqrt);
-	}
-end:
-	if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
-	    INET_ECN_set_ce(skb))
-		stats->ce_mark++;
-	return skb;
-}
 #endif
diff --git a/include/net/codel_impl.h b/include/net/codel_impl.h
new file mode 100644
index 000000000000..d289b91dcd65
--- /dev/null
+++ b/include/net/codel_impl.h
@@ -0,0 +1,255 @@
+#ifndef __NET_SCHED_CODEL_IMPL_H
+#define __NET_SCHED_CODEL_IMPL_H
+
+/*
+ * Codel - The Controlled-Delay Active Queue Management algorithm
+ *
+ *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
+ *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
+ *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
+ *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions, and the following disclaimer,
+ *    without modification.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The names of the authors may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * Alternatively, provided that this notice is retained in full, this
+ * software may be distributed under the terms of the GNU General
+ * Public License ("GPL") version 2, in which case the provisions of the
+ * GPL apply INSTEAD OF those given above.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ */
+
+/* Controlling Queue Delay (CoDel) algorithm
+ * =========================================
+ * Source : Kathleen Nichols and Van Jacobson
+ * http://queue.acm.org/detail.cfm?id=2209336
+ *
+ * Implemented on linux by Dave Taht and Eric Dumazet
+ */
+
+static void codel_params_init(struct codel_params *params)
+{
+	params->interval = MS2TIME(100);
+	params->target = MS2TIME(5);
+	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
+	params->ecn = false;
+}
+
+static void codel_vars_init(struct codel_vars *vars)
+{
+	memset(vars, 0, sizeof(*vars));
+}
+
+static void codel_stats_init(struct codel_stats *stats)
+{
+	stats->maxpacket = 0;
+}
+
+/*
+ * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
+ * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
+ *
+ * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
+ */
+static void codel_Newton_step(struct codel_vars *vars)
+{
+	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
+	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
+	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
+
+	val >>= 2; /* avoid overflow in following multiply */
+	val = (val * invsqrt) >> (32 - 2 + 1);
+
+	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
+}
+
+/*
+ * CoDel control_law is t + interval/sqrt(count)
+ * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
+ * both sqrt() and divide operation.
+ */
+static codel_time_t codel_control_law(codel_time_t t,
+				      codel_time_t interval,
+				      u32 rec_inv_sqrt)
+{
+	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
+}
+
+static bool codel_should_drop(const struct sk_buff *skb,
+			      void *ctx,
+			      struct codel_vars *vars,
+			      struct codel_params *params,
+			      struct codel_stats *stats,
+			      codel_skb_len_t skb_len_func,
+			      codel_skb_time_t skb_time_func,
+			      u32 *backlog,
+			      codel_time_t now)
+{
+	bool ok_to_drop;
+	u32 skb_len;
+
+	if (!skb) {
+		vars->first_above_time = 0;
+		return false;
+	}
+
+	skb_len = skb_len_func(skb);
+	vars->ldelay = now - skb_time_func(skb);
+
+	if (unlikely(skb_len > stats->maxpacket))
+		stats->maxpacket = skb_len;
+
+	if (codel_time_before(vars->ldelay, params->target) ||
+	    *backlog <= params->mtu) {
+		/* went below - stay below for at least interval */
+		vars->first_above_time = 0;
+		return false;
+	}
+	ok_to_drop = false;
+	if (vars->first_above_time == 0) {
+		/* just went above from below. If we stay above
+		 * for at least interval we'll say it's ok to drop
+		 */
+		vars->first_above_time = now + params->interval;
+	} else if (codel_time_after(now, vars->first_above_time)) {
+		ok_to_drop = true;
+	}
+	return ok_to_drop;
+}
+
+static struct sk_buff *codel_dequeue(void *ctx,
+				     u32 *backlog,
+				     struct codel_params *params,
+				     struct codel_vars *vars,
+				     struct codel_stats *stats,
+				     codel_skb_len_t skb_len_func,
+				     codel_skb_time_t skb_time_func,
+				     codel_skb_drop_t drop_func,
+				     codel_skb_dequeue_t dequeue_func)
+{
+	struct sk_buff *skb = dequeue_func(vars, ctx);
+	codel_time_t now;
+	bool drop;
+
+	if (!skb) {
+		vars->dropping = false;
+		return skb;
+	}
+	now = codel_get_time();
+	drop = codel_should_drop(skb, ctx, vars, params, stats,
+				 skb_len_func, skb_time_func, backlog, now);
+	if (vars->dropping) {
+		if (!drop) {
+			/* sojourn time below target - leave dropping state */
+			vars->dropping = false;
+		} else if (codel_time_after_eq(now, vars->drop_next)) {
+			/* It's time for the next drop. Drop the current
+			 * packet and dequeue the next. The dequeue might
+			 * take us out of dropping state.
+			 * If not, schedule the next drop.
+			 * A large backlog might result in drop rates so high
+			 * that the next drop should happen now,
+			 * hence the while loop.
+			 */
+			while (vars->dropping &&
+			       codel_time_after_eq(now, vars->drop_next)) {
+				vars->count++; /* dont care of possible wrap
+						* since there is no more divide
+						*/
+				codel_Newton_step(vars);
+				if (params->ecn && INET_ECN_set_ce(skb)) {
+					stats->ecn_mark++;
+					vars->drop_next =
+						codel_control_law(vars->drop_next,
+								  params->interval,
+								  vars->rec_inv_sqrt);
+					goto end;
+				}
+				stats->drop_len += skb_len_func(skb);
+				drop_func(skb, ctx);
+				stats->drop_count++;
+				skb = dequeue_func(vars, ctx);
+				if (!codel_should_drop(skb, ctx,
+						       vars, params, stats,
+						       skb_len_func,
+						       skb_time_func,
+						       backlog, now)) {
+					/* leave dropping state */
+					vars->dropping = false;
+				} else {
+					/* and schedule the next drop */
+					vars->drop_next =
+						codel_control_law(vars->drop_next,
+								  params->interval,
+								  vars->rec_inv_sqrt);
+				}
+			}
+		}
+	} else if (drop) {
+		u32 delta;
+
+		if (params->ecn && INET_ECN_set_ce(skb)) {
+			stats->ecn_mark++;
+		} else {
+			stats->drop_len += skb_len_func(skb);
+			drop_func(skb, ctx);
+			stats->drop_count++;
+
+			skb = dequeue_func(vars, ctx);
+			drop = codel_should_drop(skb, ctx, vars, params,
+						 stats, skb_len_func,
+						 skb_time_func, backlog, now);
+		}
+		vars->dropping = true;
+		/* if min went above target close to when we last went below it
+		 * assume that the drop rate that controlled the queue on the
+		 * last cycle is a good starting point to control it now.
+		 */
+		delta = vars->count - vars->lastcount;
+		if (delta > 1 &&
+		    codel_time_before(now - vars->drop_next,
+				      16 * params->interval)) {
+			vars->count = delta;
+			/* we dont care if rec_inv_sqrt approximation
+			 * is not very precise :
+			 * Next Newton steps will correct it quadratically.
+			 */
+			codel_Newton_step(vars);
+		} else {
+			vars->count = 1;
+			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
+		}
+		vars->lastcount = vars->count;
+		vars->drop_next = codel_control_law(now, params->interval,
+						    vars->rec_inv_sqrt);
+	}
+end:
+	if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
+	    INET_ECN_set_ce(skb))
+		stats->ce_mark++;
+	return skb;
+}
+
+#endif
diff --git a/include/net/codel_qdisc.h b/include/net/codel_qdisc.h
new file mode 100644
index 000000000000..8144d9cd2908
--- /dev/null
+++ b/include/net/codel_qdisc.h
@@ -0,0 +1,73 @@
+#ifndef __NET_SCHED_CODEL_QDISC_H
+#define __NET_SCHED_CODEL_QDISC_H
+
+/*
+ * Codel - The Controlled-Delay Active Queue Management algorithm
+ *
+ *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
+ *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
+ *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
+ *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions, and the following disclaimer,
+ *    without modification.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The names of the authors may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * Alternatively, provided that this notice is retained in full, this
+ * software may be distributed under the terms of the GNU General
+ * Public License ("GPL") version 2, in which case the provisions of the
+ * GPL apply INSTEAD OF those given above.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ */
+
+/* Controlling Queue Delay (CoDel) algorithm
+ * =========================================
+ * Source : Kathleen Nichols and Van Jacobson
+ * http://queue.acm.org/detail.cfm?id=2209336
+ *
+ * Implemented on linux by Dave Taht and Eric Dumazet
+ */
+
+/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
+struct codel_skb_cb {
+	codel_time_t enqueue_time;
+};
+
+static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
+{
+	qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
+	return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
+{
+	return get_codel_cb(skb)->enqueue_time;
+}
+
+static void codel_set_enqueue_time(struct sk_buff *skb)
+{
+	get_codel_cb(skb)->enqueue_time = codel_get_time();
+}
+
+#endif
diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index 512a94abe351..dddf3bb65a32 100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -49,6 +49,8 @@
 #include <linux/prefetch.h>
 #include <net/pkt_sched.h>
 #include <net/codel.h>
+#include <net/codel_impl.h>
+#include <net/codel_qdisc.h>
 
 
 #define DEFAULT_CODEL_LIMIT 1000
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index dcf7266e6901..a5e420b3d4ab 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -24,6 +24,8 @@
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
 #include <net/codel.h>
+#include <net/codel_impl.h>
+#include <net/codel_qdisc.h>
 
 /*	Fair Queue CoDel.
  *
-- 
2.1.4

Re: [PATCH 0/2] codel: make it reuseable beyond qdiscs

[David Miller]

From: Michal Kazior <michal.kazior@tieto.com>
Date: Fri, 22 Apr 2016 14:15:57 +0200

> There's an ongoing effort in fixing wireless
> bufferbloat. As part of that fq_codel is being
> ported into mac80211. To prevent code duplication
> codel.h needs to be slightly modified before it
> can be used in mac80211 (or other drivers FWIW).
> 
> For more background please see:
> 
>   https://www.spinics.net/lists/linux-wireless/msg149976.html

Series applied, but I reserve the right the revert this if the
indirect functions calling this introduces causes performance
regressions.

Thanks.