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>
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@ -8,7 +8,7 @@
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#include <net/inet_ecn.h>
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#include <net/pkt_sched.h>
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#define MAX_PROB U64_MAX
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#define MAX_PROB (U64_MAX >> BITS_PER_BYTE)
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#define DTIME_INVALID U64_MAX
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#define QUEUE_THRESHOLD 16384
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#define DQCOUNT_INVALID -1
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@ -47,7 +47,6 @@ struct pie_params {
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* @dq_count: number of bytes dequeued in a measurement cycle
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* @avg_dq_rate: calculated average dq rate
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* @backlog_old: queue backlog during previous qdelay calculation
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* @accu_prob_overflows: number of times accu_prob overflows
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*/
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struct pie_vars {
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psched_time_t qdelay;
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@ -59,7 +58,6 @@ struct pie_vars {
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u64 dq_count;
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u32 avg_dq_rate;
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u32 backlog_old;
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u8 accu_prob_overflows;
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};
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/**
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@ -107,7 +105,6 @@ static inline void pie_vars_init(struct pie_vars *vars)
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vars->accu_prob = 0;
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vars->dq_count = DQCOUNT_INVALID;
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vars->avg_dq_rate = 0;
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vars->accu_prob_overflows = 0;
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}
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static inline struct pie_skb_cb *get_pie_cb(const struct sk_buff *skb)
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@ -189,7 +189,6 @@ static int fq_pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
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out:
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q->stats.dropped++;
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sel_flow->vars.accu_prob = 0;
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sel_flow->vars.accu_prob_overflows = 0;
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__qdisc_drop(skb, to_free);
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qdisc_qstats_drop(sch);
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return NET_XMIT_CN;
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@ -62,27 +62,19 @@ bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
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else
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local_prob = vars->prob;
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if (local_prob == 0) {
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if (local_prob == 0)
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vars->accu_prob = 0;
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vars->accu_prob_overflows = 0;
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}
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else
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vars->accu_prob += local_prob;
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if (local_prob > MAX_PROB - vars->accu_prob)
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vars->accu_prob_overflows++;
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vars->accu_prob += local_prob;
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if (vars->accu_prob_overflows == 0 &&
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vars->accu_prob < (MAX_PROB / 100) * 85)
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if (vars->accu_prob < (MAX_PROB / 100) * 85)
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return false;
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if (vars->accu_prob_overflows == 8 &&
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vars->accu_prob >= MAX_PROB / 2)
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if (vars->accu_prob >= (MAX_PROB / 2) * 17)
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return true;
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prandom_bytes(&rnd, 8);
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if (rnd < local_prob) {
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if ((rnd >> BITS_PER_BYTE) < local_prob) {
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vars->accu_prob = 0;
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vars->accu_prob_overflows = 0;
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return true;
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}
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@ -129,7 +121,6 @@ static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
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out:
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q->stats.dropped++;
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q->vars.accu_prob = 0;
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q->vars.accu_prob_overflows = 0;
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return qdisc_drop(skb, sch, to_free);
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}
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