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authorEric Dumazet <edumazet@google.com>2016-09-19 23:39:11 -0400
committerDavid S. Miller <davem@davemloft.net>2016-09-21 00:23:00 -0400
commit77879147a3481babffd7e368d977ab682545a6bd (patch)
tree394b9e60b29282a5e68fcdb852db6d508bc569af /net/sched/sch_fq.c
parenttcp: use windowed min filter library for TCP min_rtt estimation (diff)
downloadlinux-dev-77879147a3481babffd7e368d977ab682545a6bd.tar.xz
linux-dev-77879147a3481babffd7e368d977ab682545a6bd.zip
net_sched: sch_fq: add low_rate_threshold parameter
This commit adds to the fq module a low_rate_threshold parameter to insert a delay after all packets if the socket requests a pacing rate below the threshold. This helps achieve more precise control of the sending rate with low-rate paths, especially policers. The basic issue is that if a congestion control module detects a policer at a certain rate, it may want fq to be able to shape to that policed rate. That way the sender can avoid policer drops by having the packets arrive at the policer at or just under the policed rate. The default threshold of 550Kbps was chosen analytically so that for policers or links at 500Kbps or 512Kbps fq would very likely invoke this mechanism, even if the pacing rate was briefly slightly above the available bandwidth. This value was then empirically validated with two years of production testing on YouTube video servers. Signed-off-by: Van Jacobson <vanj@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Nandita Dukkipati <nanditad@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched/sch_fq.c')
-rw-r--r--net/sched/sch_fq.c22
1 files changed, 19 insertions, 3 deletions
diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index dc52cc10d6ed..5dd929cc1423 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -94,6 +94,7 @@ struct fq_sched_data {
u32 flow_max_rate; /* optional max rate per flow */
u32 flow_plimit; /* max packets per flow */
u32 orphan_mask; /* mask for orphaned skb */
+ u32 low_rate_threshold;
struct rb_root *fq_root;
u8 rate_enable;
u8 fq_trees_log;
@@ -433,7 +434,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
struct fq_flow_head *head;
struct sk_buff *skb;
struct fq_flow *f;
- u32 rate;
+ u32 rate, plen;
skb = fq_dequeue_head(sch, &q->internal);
if (skb)
@@ -482,7 +483,7 @@ begin:
prefetch(&skb->end);
f->credit -= qdisc_pkt_len(skb);
- if (f->credit > 0 || !q->rate_enable)
+ if (!q->rate_enable)
goto out;
/* Do not pace locally generated ack packets */
@@ -493,8 +494,15 @@ begin:
if (skb->sk)
rate = min(skb->sk->sk_pacing_rate, rate);
+ if (rate <= q->low_rate_threshold) {
+ f->credit = 0;
+ plen = qdisc_pkt_len(skb);
+ } else {
+ plen = max(qdisc_pkt_len(skb), q->quantum);
+ if (f->credit > 0)
+ goto out;
+ }
if (rate != ~0U) {
- u32 plen = max(qdisc_pkt_len(skb), q->quantum);
u64 len = (u64)plen * NSEC_PER_SEC;
if (likely(rate))
@@ -662,6 +670,7 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
[TCA_FQ_FLOW_MAX_RATE] = { .type = NLA_U32 },
[TCA_FQ_BUCKETS_LOG] = { .type = NLA_U32 },
[TCA_FQ_FLOW_REFILL_DELAY] = { .type = NLA_U32 },
+ [TCA_FQ_LOW_RATE_THRESHOLD] = { .type = NLA_U32 },
};
static int fq_change(struct Qdisc *sch, struct nlattr *opt)
@@ -716,6 +725,10 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt)
if (tb[TCA_FQ_FLOW_MAX_RATE])
q->flow_max_rate = nla_get_u32(tb[TCA_FQ_FLOW_MAX_RATE]);
+ if (tb[TCA_FQ_LOW_RATE_THRESHOLD])
+ q->low_rate_threshold =
+ nla_get_u32(tb[TCA_FQ_LOW_RATE_THRESHOLD]);
+
if (tb[TCA_FQ_RATE_ENABLE]) {
u32 enable = nla_get_u32(tb[TCA_FQ_RATE_ENABLE]);
@@ -781,6 +794,7 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt)
q->fq_root = NULL;
q->fq_trees_log = ilog2(1024);
q->orphan_mask = 1024 - 1;
+ q->low_rate_threshold = 550000 / 8;
qdisc_watchdog_init(&q->watchdog, sch);
if (opt)
@@ -811,6 +825,8 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
nla_put_u32(skb, TCA_FQ_FLOW_REFILL_DELAY,
jiffies_to_usecs(q->flow_refill_delay)) ||
nla_put_u32(skb, TCA_FQ_ORPHAN_MASK, q->orphan_mask) ||
+ nla_put_u32(skb, TCA_FQ_LOW_RATE_THRESHOLD,
+ q->low_rate_threshold) ||
nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log))
goto nla_put_failure;