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pie: remove pie_vars->accu_prob_overflows

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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>
This commit is contained in:
Leslie Monis
2020-03-05 00:26:01 +05:30
committed by David S. Miller
parent 220d4ac74e
commit 105e808c1d
3 changed files with 7 additions and 20 deletions
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5
include/net/pie.h
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@@ -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)