From: Leslie Monis <lesliemonis@gmail.com>
To: netdev@vger.kernel.org
Cc: davem@davemloft.net, tahiliani@nitk.edu.in, gautamramk@gmail.com
Subject: [PATCH net-next v2 3/4] pie: remove pie_vars->accu_prob_overflows
Date: Thu, 5 Mar 2020 00:26:01 +0530 [thread overview]
Message-ID: <20200304185602.2540-4-lesliemonis@gmail.com> (raw)
In-Reply-To: <20200304185602.2540-1-lesliemonis@gmail.com>
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>
---
include/net/pie.h | 5 +----
net/sched/sch_fq_pie.c | 1 -
net/sched/sch_pie.c | 21 ++++++---------------
3 files changed, 7 insertions(+), 20 deletions(-)
diff --git a/include/net/pie.h b/include/net/pie.h
index 24f68c1e9919..1c645b76a2ed 100644
--- 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 214657eb3dfd..a9da8776bf5b 100644
--- 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 198cfa34a00a..f52442d39bf5 100644
--- 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);
}
--
2.17.1
next prev parent reply other threads:[~2020-03-04 18:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-04 18:55 [PATCH net-next v2 0/4] pie: minor improvements Leslie Monis
2020-03-04 18:55 ` [PATCH net-next v2 1/4] pie: use term backlog instead of qlen Leslie Monis
2020-03-04 18:56 ` [PATCH net-next v2 2/4] pie: remove unnecessary type casting Leslie Monis
2020-03-04 18:56 ` Leslie Monis [this message]
2020-03-04 18:56 ` [PATCH net-next v2 4/4] pie: realign comment Leslie Monis
2020-03-04 20:49 ` [PATCH net-next v2 0/4] pie: minor improvements Jakub Kicinski
2020-03-04 21:26 ` David Miller
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