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Date: Mon, 25 Feb 2019 15:50:49 +0530
From: Leslie Monis <lesliemonis@...il.com>
To: jhs@...atatu.com
Cc: netdev@...r.kernel.org, dave@...t.net,
"Mohit P. Tahiliani" <tahiliani@...k.edu.in>,
Dhaval Khandla <dhavaljkhandla26@...il.com>,
Hrishikesh Hiraskar <hrishihiraskar@...il.com>,
Manish Kumar B <bmanish15597@...il.com>,
"Sachin D . Patil" <sdp.sachin@...il.com>,
Leslie Monis <lesliemonis@...il.com>
Subject: [PATCH net-next v2 5/7] net: sched: pie: add more cases to auto-tune alpha and beta
From: "Mohit P. Tahiliani" <tahiliani@...k.edu.in>
The current implementation scales the local alpha and beta
variables in the calculate_probability function by the same
amount for all values of drop probability below 1%.
RFC 8033 suggests using additional cases for auto-tuning
alpha and beta when the drop probability is less than 1%.
In order to add more auto-tuning cases, MAX_PROB must be
scaled by u64 instead of u32 to prevent underflow when
scaling the local alpha and beta variables in the
calculate_probability function.
Signed-off-by: Mohit P. Tahiliani <tahiliani@...k.edu.in>
Signed-off-by: Dhaval Khandla <dhavaljkhandla26@...il.com>
Signed-off-by: Hrishikesh Hiraskar <hrishihiraskar@...il.com>
Signed-off-by: Manish Kumar B <bmanish15597@...il.com>
Signed-off-by: Sachin D. Patil <sdp.sachin@...il.com>
Signed-off-by: Leslie Monis <lesliemonis@...il.com>
---
include/uapi/linux/pkt_sched.h | 2 +-
net/sched/sch_pie.c | 65 +++++++++++++++++-----------------
2 files changed, 33 insertions(+), 34 deletions(-)
diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 0d18b1d1fbbc..1eb572ef3f27 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -954,7 +954,7 @@ enum {
#define TCA_PIE_MAX (__TCA_PIE_MAX - 1)
struct tc_pie_xstats {
- __u32 prob; /* current probability */
+ __u64 prob; /* current probability */
__u32 delay; /* current delay in ms */
__u32 avg_dq_rate; /* current average dq_rate in bits/pie_time */
__u32 packets_in; /* total number of packets enqueued */
diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index d88ab53593b3..b9f586cfb51c 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -33,7 +33,7 @@
#define QUEUE_THRESHOLD 16384
#define DQCOUNT_INVALID -1
-#define MAX_PROB 0xffffffff
+#define MAX_PROB 0xffffffffffffffff
#define PIE_SCALE 8
/* parameters used */
@@ -49,7 +49,7 @@ struct pie_params {
/* variables used */
struct pie_vars {
- u32 prob; /* probability but scaled by u32 limit. */
+ u64 prob; /* probability but scaled by u64 limit. */
psched_time_t burst_time;
psched_time_t qdelay;
psched_time_t qdelay_old;
@@ -99,8 +99,8 @@ static void pie_vars_init(struct pie_vars *vars)
static bool drop_early(struct Qdisc *sch, u32 packet_size)
{
struct pie_sched_data *q = qdisc_priv(sch);
- u32 rnd;
- u32 local_prob = q->vars.prob;
+ u64 rnd;
+ u64 local_prob = q->vars.prob;
u32 mtu = psched_mtu(qdisc_dev(sch));
/* If there is still burst allowance left skip random early drop */
@@ -124,11 +124,11 @@ static bool drop_early(struct Qdisc *sch, u32 packet_size)
* probablity. Smaller packets will have lower drop prob in this case
*/
if (q->params.bytemode && packet_size <= mtu)
- local_prob = (local_prob / mtu) * packet_size;
+ local_prob = (local_prob / (u64)mtu) * (u64)packet_size;
else
local_prob = q->vars.prob;
- rnd = prandom_u32();
+ prandom_bytes(&rnd, 8);
if (rnd < local_prob)
return true;
@@ -317,9 +317,10 @@ static void calculate_probability(struct Qdisc *sch)
u32 qlen = sch->qstats.backlog; /* queue size in bytes */
psched_time_t qdelay = 0; /* in pschedtime */
psched_time_t qdelay_old = q->vars.qdelay; /* in pschedtime */
- s32 delta = 0; /* determines the change in probability */
- u32 oldprob;
- u32 alpha, beta;
+ s64 delta = 0; /* determines the change in probability */
+ u64 oldprob;
+ u64 alpha, beta;
+ u32 power;
bool update_prob = true;
q->vars.qdelay_old = q->vars.qdelay;
@@ -339,38 +340,36 @@ static void calculate_probability(struct Qdisc *sch)
* value for alpha as 0.125. In this implementation, we use values 0-32
* passed from user space to represent this. Also, alpha and beta have
* unit of HZ and need to be scaled before they can used to update
- * probability. alpha/beta are updated locally below by 1) scaling them
- * appropriately 2) scaling down by 16 to come to 0-2 range.
- * Please see paper for details.
- *
- * We scale alpha and beta differently depending on whether we are in
- * light, medium or high dropping mode.
+ * probability. alpha/beta are updated locally below by scaling down
+ * by 16 to come to 0-2 range.
*/
- if (q->vars.prob < MAX_PROB / 100) {
- alpha =
- (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
- beta =
- (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
- } else if (q->vars.prob < MAX_PROB / 10) {
- alpha =
- (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
- beta =
- (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
- } else {
- alpha =
- (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
- beta =
- (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
+ alpha = ((u64)q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
+ beta = ((u64)q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
+
+ /* We scale alpha and beta differently depending on how heavy the
+ * congestion is. Please see RFC 8033 for details.
+ */
+ if (q->vars.prob < MAX_PROB / 10) {
+ alpha >>= 1;
+ beta >>= 1;
+
+ power = 100;
+ while (q->vars.prob < MAX_PROB / (u64)power &&
+ power <= 1000000) {
+ alpha >>= 2;
+ beta >>= 2;
+ power *= 10;
+ }
}
/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
- delta += alpha * ((qdelay - q->params.target));
- delta += beta * ((qdelay - qdelay_old));
+ delta += alpha * (u64)(qdelay - q->params.target);
+ delta += beta * (u64)(qdelay - qdelay_old);
oldprob = q->vars.prob;
/* to ensure we increase probability in steps of no more than 2% */
- if (delta > (s32)(MAX_PROB / (100 / 2)) &&
+ if (delta > (s64)(MAX_PROB / (100 / 2)) &&
q->vars.prob >= MAX_PROB / 10)
delta = (MAX_PROB / 100) * 2;
--
2.17.1
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