pie: remove pie_vars->accu_prob_overflows

The variable pie_vars->accu_prob is used as an accumulator for
probability values. Since probabilty values are scaled using the
MAX_PROB macro denoting (2^64 - 1), pie_vars->accu_prob is
likely to overflow as it is of type u64.

The variable pie_vars->accu_prob_overflows counts the number of
times the variable pie_vars->accu_prob overflows.

The MAX_PROB macro needs to be equal to at least (2^39 - 1) in
order to do precise calculations without any underflow. Thus
MAX_PROB can be reduced to (2^56 - 1) without affecting the
precision in calculations drastically. Doing so will eliminate
the need for the variable pie_vars->accu_prob_overflows as the
variable pie_vars->accu_prob will never overflow.

Removing the variable pie_vars->accu_prob_overflows also reduces
the size of the structure pie_vars to exactly 64 bytes.

Signed-off-by: Mohit P. Tahiliani <tahiliani@nitk.edu.in>
Signed-off-by: Gautam Ramakrishnan <gautamramk@gmail.com>
Signed-off-by: Leslie Monis <lesliemonis@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/pie.h b/include/net/pie.h
index 24f68c1..1c645b7 100644 (file)
--- a/include/net/pie.h
+++ b/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
@@ -47,7 +47,6 @@ struct pie_params {
  * @dq_count:                  number of bytes dequeued in a measurement cycle
  * @avg_dq_rate:               calculated average dq rate
  * @backlog_old:               queue backlog during previous qdelay calculation
- * @accu_prob_overflows:       number of times accu_prob overflows
  */
 struct pie_vars {
        psched_time_t qdelay;
@@ -59,7 +58,6 @@ struct pie_vars {
        u64 dq_count;
        u32 avg_dq_rate;
        u32 backlog_old;
-       u8 accu_prob_overflows;
 };
 
 /**
@@ -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)

diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c
index 214657e..a9da877 100644 (file)
--- a/net/sched/sch_fq_pie.c
+++ b/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;

diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index 198cfa3..f52442d 100644 (file)
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -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++;
-
-       vars->accu_prob += local_prob;
+       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);
 }