Commit 105e808c authored by Leslie Monis's avatar Leslie Monis Committed by David S. Miller
Browse files

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: default avatarMohit P. Tahiliani <tahiliani@nitk.edu.in>
Signed-off-by: default avatarGautam Ramakrishnan <gautamramk@gmail.com>
Signed-off-by: default avatarLeslie Monis <lesliemonis@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 220d4ac7

include/net/pie.h

+1 −4
Original line number Diff line number Diff line
@@ -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)

net/sched/sch_fq_pie.c

+0 −1
Original line number Diff line number Diff line
@@ -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

+6 −15
Original line number Diff line number Diff line
@@ -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);

}

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