* [PATCH net-next 0/4] pie: minor improvements
@ 2020-03-02 15:18 Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 1/4] pie: use term backlog instead of qlen Leslie Monis
` (3 more replies)
0 siblings, 4 replies; 6+ messages in thread
From: Leslie Monis @ 2020-03-02 15:18 UTC (permalink / raw)
To: netdev; +Cc: davem, tahiliani, gautamramk
This patch series includes the following minor changes with
respect to the PIE/FQ-PIE qdiscs:
- Patch 1 removes some ambiguity by using the term "backlog"
instead of "qlen" when referring to the queue length
in bytes.
- Patch 2 removes redundant type casting on two expressions.
- Patch 3 removes the pie_vars->accu_prob_overflows variable
without affecting the precision in calculations and
makes the size of the pie_vars structure exactly 64
bytes.
- Patch 4 realigns a comment affected by a change in patch 3.
Leslie Monis (4):
pie: use term backlog instead of qlen
pie: remove unnecessary type casting
pie: remove pie_vars->accu_prob_overflows
pie: realign comment
include/net/pie.h | 31 +++++++++++++---------------
net/sched/sch_fq_pie.c | 1 -
net/sched/sch_pie.c | 47 +++++++++++++++++-------------------------
3 files changed, 33 insertions(+), 46 deletions(-)
--
2.17.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH net-next 1/4] pie: use term backlog instead of qlen
2020-03-02 15:18 [PATCH net-next 0/4] pie: minor improvements Leslie Monis
@ 2020-03-02 15:18 ` Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 2/4] pie: remove unnecessary type casting Leslie Monis
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Leslie Monis @ 2020-03-02 15:18 UTC (permalink / raw)
To: netdev; +Cc: davem, tahiliani, gautamramk
Remove ambiguity by using the term backlog instead of qlen when
representing the queue length in 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 | 10 +++++-----
net/sched/sch_pie.c | 22 +++++++++++-----------
2 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/include/net/pie.h b/include/net/pie.h
index fd5a37cb7993..24f68c1e9919 100644
--- a/include/net/pie.h
+++ b/include/net/pie.h
@@ -46,7 +46,7 @@ struct pie_params {
* @accu_prob: accumulated drop probability
* @dq_count: number of bytes dequeued in a measurement cycle
* @avg_dq_rate: calculated average dq rate
- * @qlen_old: queue length during previous qdelay calculation
+ * @backlog_old: queue backlog during previous qdelay calculation
* @accu_prob_overflows: number of times accu_prob overflows
*/
struct pie_vars {
@@ -58,7 +58,7 @@ struct pie_vars {
u64 accu_prob;
u64 dq_count;
u32 avg_dq_rate;
- u32 qlen_old;
+ u32 backlog_old;
u8 accu_prob_overflows;
};
@@ -127,12 +127,12 @@ static inline void pie_set_enqueue_time(struct sk_buff *skb)
}
bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
- struct pie_vars *vars, u32 qlen, u32 packet_size);
+ struct pie_vars *vars, u32 backlog, u32 packet_size);
void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
- struct pie_vars *vars, u32 qlen);
+ struct pie_vars *vars, u32 backlog);
void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
- u32 qlen);
+ u32 backlog);
#endif
diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index 915bcdb59a9f..8a2f9f11c86f 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -31,7 +31,7 @@ struct pie_sched_data {
};
bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
- struct pie_vars *vars, u32 qlen, u32 packet_size)
+ struct pie_vars *vars, u32 backlog, u32 packet_size)
{
u64 rnd;
u64 local_prob = vars->prob;
@@ -51,7 +51,7 @@ bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
/* If we have fewer than 2 mtu-sized packets, disable pie_drop_early,
* similar to min_th in RED
*/
- if (qlen < 2 * mtu)
+ if (backlog < 2 * mtu)
return false;
/* If bytemode is turned on, use packet size to compute new
@@ -215,7 +215,7 @@ static int pie_change(struct Qdisc *sch, struct nlattr *opt,
}
void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
- struct pie_vars *vars, u32 qlen)
+ struct pie_vars *vars, u32 backlog)
{
psched_time_t now = psched_get_time();
u32 dtime = 0;
@@ -231,7 +231,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
vars->dq_tstamp = now;
- if (qlen == 0)
+ if (backlog == 0)
vars->qdelay = 0;
if (dtime == 0)
@@ -244,7 +244,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
* we have enough packets to calculate the drain rate. Save
* current time as dq_tstamp and start measurement cycle.
*/
- if (qlen >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
+ if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
vars->dq_tstamp = psched_get_time();
vars->dq_count = 0;
}
@@ -283,7 +283,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
* dq_count to 0 to re-enter the if block when the next
* packet is dequeued
*/
- if (qlen < QUEUE_THRESHOLD) {
+ if (backlog < QUEUE_THRESHOLD) {
vars->dq_count = DQCOUNT_INVALID;
} else {
vars->dq_count = 0;
@@ -307,7 +307,7 @@ void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
EXPORT_SYMBOL_GPL(pie_process_dequeue);
void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
- u32 qlen)
+ u32 backlog)
{
psched_time_t qdelay = 0; /* in pschedtime */
psched_time_t qdelay_old = 0; /* in pschedtime */
@@ -322,7 +322,7 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
vars->qdelay_old = vars->qdelay;
if (vars->avg_dq_rate > 0)
- qdelay = (qlen << PIE_SCALE) / vars->avg_dq_rate;
+ qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate;
else
qdelay = 0;
} else {
@@ -330,10 +330,10 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
qdelay_old = vars->qdelay_old;
}
- /* If qdelay is zero and qlen is not, it means qlen is very small,
+ /* If qdelay is zero and backlog is not, it means backlog is very small,
* so we do not update probabilty in this round.
*/
- if (qdelay == 0 && qlen != 0)
+ if (qdelay == 0 && backlog != 0)
update_prob = false;
/* In the algorithm, alpha and beta are between 0 and 2 with typical
@@ -409,7 +409,7 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
vars->prob -= vars->prob / 64;
vars->qdelay = qdelay;
- vars->qlen_old = qlen;
+ vars->backlog_old = backlog;
/* We restart the measurement cycle if the following conditions are met
* 1. If the delay has been low for 2 consecutive Tupdate periods
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 2/4] pie: remove unnecessary type casting
2020-03-02 15:18 [PATCH net-next 0/4] pie: minor improvements Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 1/4] pie: use term backlog instead of qlen Leslie Monis
@ 2020-03-02 15:18 ` Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 4/4] pie: realign comment Leslie Monis
3 siblings, 0 replies; 6+ messages in thread
From: Leslie Monis @ 2020-03-02 15:18 UTC (permalink / raw)
To: netdev; +Cc: davem, tahiliani, gautamramk
In function pie_calculate_probability(), the variables alpha and
beta are of type u64. The variables qdelay, qdelay_old and
params->target are of type psched_time_t (which is also u64).
The explicit type casting done when calculating the value for
the variable delta is redundant and not required.
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>
---
net/sched/sch_pie.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index 8a2f9f11c86f..198cfa34a00a 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -363,8 +363,8 @@ void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
}
/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
- delta += alpha * (u64)(qdelay - params->target);
- delta += beta * (u64)(qdelay - qdelay_old);
+ delta += alpha * (qdelay - params->target);
+ delta += beta * (qdelay - qdelay_old);
oldprob = vars->prob;
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows
2020-03-02 15:18 [PATCH net-next 0/4] pie: minor improvements Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 1/4] pie: use term backlog instead of qlen Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 2/4] pie: remove unnecessary type casting Leslie Monis
@ 2020-03-02 15:18 ` Leslie Monis
2020-03-04 1:43 ` David Miller
2020-03-02 15:18 ` [PATCH net-next 4/4] pie: realign comment Leslie Monis
3 siblings, 1 reply; 6+ messages in thread
From: Leslie Monis @ 2020-03-02 15:18 UTC (permalink / raw)
To: netdev; +Cc: davem, tahiliani, gautamramk
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..718ac61f4d47 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);
+ prandom_bytes(&rnd, 7);
if (rnd < 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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 4/4] pie: realign comment
2020-03-02 15:18 [PATCH net-next 0/4] pie: minor improvements Leslie Monis
` (2 preceding siblings ...)
2020-03-02 15:18 ` [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows Leslie Monis
@ 2020-03-02 15:18 ` Leslie Monis
3 siblings, 0 replies; 6+ messages in thread
From: Leslie Monis @ 2020-03-02 15:18 UTC (permalink / raw)
To: netdev; +Cc: davem, tahiliani, gautamramk
Realign a comment after the change introduced by the
previous patch.
Signed-off-by: Leslie Monis <lesliemonis@gmail.com>
---
include/net/pie.h | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/include/net/pie.h b/include/net/pie.h
index 1c645b76a2ed..3fe2361e03b4 100644
--- a/include/net/pie.h
+++ b/include/net/pie.h
@@ -38,15 +38,15 @@ struct pie_params {
/**
* struct pie_vars - contains pie variables
- * @qdelay: current queue delay
- * @qdelay_old: queue delay in previous qdelay calculation
- * @burst_time: burst time allowance
- * @dq_tstamp: timestamp at which dq rate was last calculated
- * @prob: drop probability
- * @accu_prob: accumulated drop probability
- * @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
+ * @qdelay: current queue delay
+ * @qdelay_old: queue delay in previous qdelay calculation
+ * @burst_time: burst time allowance
+ * @dq_tstamp: timestamp at which dq rate was last calculated
+ * @prob: drop probability
+ * @accu_prob: accumulated drop probability
+ * @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
*/
struct pie_vars {
psched_time_t qdelay;
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows
2020-03-02 15:18 ` [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows Leslie Monis
@ 2020-03-04 1:43 ` David Miller
0 siblings, 0 replies; 6+ messages in thread
From: David Miller @ 2020-03-04 1:43 UTC (permalink / raw)
To: lesliemonis; +Cc: netdev, tahiliani, gautamramk
From: Leslie Monis <lesliemonis@gmail.com>
Date: Mon, 2 Mar 2020 20:48:30 +0530
> - prandom_bytes(&rnd, 8);
> + prandom_bytes(&rnd, 7);
This is undefined because it depends upon the endianness whether you
are initializing the more significant 7 bytes or the least significant
7 bytes of rnd.
I think you should just keep this at 8 and explicitly clear out the
top byte.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2020-03-02 15:18 [PATCH net-next 0/4] pie: minor improvements Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 1/4] pie: use term backlog instead of qlen Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 2/4] pie: remove unnecessary type casting Leslie Monis
2020-03-02 15:18 ` [PATCH net-next 3/4] pie: remove pie_vars->accu_prob_overflows Leslie Monis
2020-03-04 1:43 ` David Miller
2020-03-02 15:18 ` [PATCH net-next 4/4] pie: realign comment Leslie Monis
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