Merge branch 'pie-minor-improvements'

Leslie Monis says:

====================
pie: minor improvements

This patch series includes the following minor changes with
respect to the PIE/FQ-PIE qdiscs:

 - Patch 1 removes some ambiguity by using the term "backlog"
           instead of "qlen" when referring to the queue length
           in bytes.
 - Patch 2 removes redundant type casting on two expressions.
 - Patch 3 removes the pie_vars->accu_prob_overflows variable
           without affecting the precision in calculations and
           makes the size of the pie_vars structure exactly 64
           bytes.
 - Patch 4 realigns a comment affected by a change in patch 3.

Changes from v1 to v2:
 - Kept 8 as the argument to prandom_bytes() instead of changing it
   to 7 as suggested by David Miller.
====================
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pie.h

@@ -8,7 +8,7 @@
 #include <net/inet_ecn.h>
 #include <net/pkt_sched.h>
 
-#define MAX_PROB	U64_MAX
+#define MAX_PROB	(U64_MAX >> BITS_PER_BYTE)
 #define DTIME_INVALID	U64_MAX
 #define QUEUE_THRESHOLD	16384
 #define DQCOUNT_INVALID	-1
@@ -46,8 +46,7 @@ struct pie_params {
  * @accu_prob:		accumulated drop probability
  * @dq_count:		number of bytes dequeued in a measurement cycle
  * @avg_dq_rate:	calculated average dq rate
- * @qlen_old:			queue length during previous qdelay calculation
- * @accu_prob_overflows:	number of times accu_prob overflows
+ * @backlog_old:	queue backlog during previous qdelay calculation
  */
 struct pie_vars {
 	psched_time_t qdelay;
@@ -58,8 +57,7 @@ struct pie_vars {
 	u64 accu_prob;
 	u64 dq_count;
 	u32 avg_dq_rate;
-	u32 qlen_old;
-	u8 accu_prob_overflows;
+	u32 backlog_old;
 };
 
 /**
@@ -107,7 +105,6 @@ static inline void pie_vars_init(struct pie_vars *vars)
 	vars->accu_prob = 0;
 	vars->dq_count = DQCOUNT_INVALID;
 	vars->avg_dq_rate = 0;
-	vars->accu_prob_overflows = 0;
 }
 
 static inline struct pie_skb_cb *get_pie_cb(const struct sk_buff *skb)
@@ -127,12 +124,12 @@ static inline void pie_set_enqueue_time(struct sk_buff *skb)
 }
 
 bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
-		    struct pie_vars *vars, u32 qlen, u32 packet_size);
+		    struct pie_vars *vars, u32 backlog, u32 packet_size);
 
 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
-			 struct pie_vars *vars, u32 qlen);
+			 struct pie_vars *vars, u32 backlog);
 
 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
-			       u32 qlen);
+			       u32 backlog);
 
 #endif

net/sched/sch_fq_pie.c

@@ -189,7 +189,6 @@ static int fq_pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 out:
 	q->stats.dropped++;
 	sel_flow->vars.accu_prob = 0;
-	sel_flow->vars.accu_prob_overflows = 0;
 	__qdisc_drop(skb, to_free);
 	qdisc_qstats_drop(sch);
 	return NET_XMIT_CN;

net/sched/sch_pie.c

@@ -31,7 +31,7 @@ struct pie_sched_data {
 };
 
 bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
-		    struct pie_vars *vars, u32 qlen, u32 packet_size)
+		    struct pie_vars *vars, u32 backlog, u32 packet_size)
 {
 	u64 rnd;
 	u64 local_prob = vars->prob;
@@ -51,7 +51,7 @@ bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
 	/* If we have fewer than 2 mtu-sized packets, disable pie_drop_early,
 	 * similar to min_th in RED
 	 */
-	if (qlen < 2 * mtu)
+	if (backlog < 2 * mtu)
 		return false;
 
 	/* If bytemode is turned on, use packet size to compute new
@@ -62,27 +62,19 @@ bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
 	else
 		local_prob = vars->prob;
 
-	if (local_prob == 0) {
+	if (local_prob == 0)
 		vars->accu_prob = 0;
-		vars->accu_prob_overflows = 0;
-	}
-
-	if (local_prob > MAX_PROB - vars->accu_prob)
-		vars->accu_prob_overflows++;
-
+	else
 		vars->accu_prob += local_prob;
 
-	if (vars->accu_prob_overflows == 0 &&
-	    vars->accu_prob < (MAX_PROB / 100) * 85)
+	if (vars->accu_prob < (MAX_PROB / 100) * 85)
 		return false;
-	if (vars->accu_prob_overflows == 8 &&
-	    vars->accu_prob >= MAX_PROB / 2)
+	if (vars->accu_prob >= (MAX_PROB / 2) * 17)
 		return true;
 
 	prandom_bytes(&rnd, 8);
-	if (rnd < local_prob) {
+	if ((rnd >> BITS_PER_BYTE) < local_prob) {
 		vars->accu_prob = 0;
-		vars->accu_prob_overflows = 0;
 		return true;
 	}
 
@@ -129,7 +121,6 @@ static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 out:
 	q->stats.dropped++;
 	q->vars.accu_prob = 0;
-	q->vars.accu_prob_overflows = 0;
 	return qdisc_drop(skb, sch, to_free);
 }
 
@@ -215,7 +206,7 @@ static int pie_change(struct Qdisc *sch, struct nlattr *opt,
 }
 
 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
-			 struct pie_vars *vars, u32 qlen)
+			 struct pie_vars *vars, u32 backlog)
 {
 	psched_time_t now = psched_get_time();
 	u32 dtime = 0;
@@ -231,7 +222,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
 
 		vars->dq_tstamp = now;
 
-		if (qlen == 0)
+		if (backlog == 0)
 			vars->qdelay = 0;
 
 		if (dtime == 0)
@@ -244,7 +235,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
 	 * we have enough packets to calculate the drain rate. Save
 	 * current time as dq_tstamp and start measurement cycle.
 	 */
-	if (qlen >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
+	if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
 		vars->dq_tstamp = psched_get_time();
 		vars->dq_count = 0;
 	}
@@ -283,7 +274,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
 			 * dq_count to 0 to re-enter the if block when the next
 			 * packet is dequeued
 			 */
-			if (qlen < QUEUE_THRESHOLD) {
+			if (backlog < QUEUE_THRESHOLD) {
 				vars->dq_count = DQCOUNT_INVALID;
 			} else {
 				vars->dq_count = 0;
@@ -307,7 +298,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
 EXPORT_SYMBOL_GPL(pie_process_dequeue);
 
 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
-			       u32 qlen)
+			       u32 backlog)
 {
 	psched_time_t qdelay = 0;	/* in pschedtime */
 	psched_time_t qdelay_old = 0;	/* in pschedtime */
@@ -322,7 +313,7 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
 		vars->qdelay_old = vars->qdelay;
 
 		if (vars->avg_dq_rate > 0)
-			qdelay = (qlen << PIE_SCALE) / vars->avg_dq_rate;
+			qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate;
 		else
 			qdelay = 0;
 	} else {
@@ -330,10 +321,10 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
 		qdelay_old = vars->qdelay_old;
 	}
 
-	/* If qdelay is zero and qlen is not, it means qlen is very small,
+	/* If qdelay is zero and backlog is not, it means backlog is very small,
 	 * so we do not update probabilty in this round.
 	 */
-	if (qdelay == 0 && qlen != 0)
+	if (qdelay == 0 && backlog != 0)
 		update_prob = false;
 
 	/* In the algorithm, alpha and beta are between 0 and 2 with typical
@@ -363,8 +354,8 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
 	}
 
 	/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
-	delta += alpha * (u64)(qdelay - params->target);
-	delta += beta * (u64)(qdelay - qdelay_old);
+	delta += alpha * (qdelay - params->target);
+	delta += beta * (qdelay - qdelay_old);
 
 	oldprob = vars->prob;
 
@@ -409,7 +400,7 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
 		vars->prob -= vars->prob / 64;
 
 	vars->qdelay = qdelay;
-	vars->qlen_old = qlen;
+	vars->backlog_old = backlog;
 
 	/* We restart the measurement cycle if the following conditions are met
 	 * 1. If the delay has been low for 2 consecutive Tupdate periods