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net_sched: sch_fq: add horizon attribute
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QUIC servers would like to use SO_TXTIME, without having CAP_NET_ADMIN,
to efficiently pace UDP packets.

As far as sch_fq is concerned, we need to add safety checks, so
that a buggy application does not fill the qdisc with packets
having delivery time far in the future.

This patch adds a configurable horizon (default: 10 seconds),
and a configurable policy when a packet is beyond the horizon
at enqueue() time:
- either drop the packet (default policy)
- or cap its delivery time to the horizon.

$ tc -s -d qd sh dev eth0
qdisc fq 8022: root refcnt 257 limit 10000p flow_limit 100p buckets 1024
 orphan_mask 1023 quantum 10Kb initial_quantum 51160b low_rate_threshold 550Kbit
 refill_delay 40.0ms timer_slack 10.000us horizon 10.000s
 Sent 1234215879 bytes 837099 pkt (dropped 21, overlimits 0 requeues 6)
 backlog 0b 0p requeues 6
  flows 1191 (inactive 1177 throttled 0)
  gc 0 highprio 0 throttled 692 latency 11.480us
  pkts_too_long 0 alloc_errors 0 horizon_drops 21 horizon_caps 0

v2: fixed an overflow on 32bit kernels in fq_init(), reported
    by kbuild test robot <[email protected]>

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
Eric Dumazet authored and davem330 committed May 4, 2020
1 parent bf6dba7 commit 39d0105
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Showing 2 changed files with 60 additions and 5 deletions.
6 changes: 6 additions & 0 deletions include/uapi/linux/pkt_sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -913,6 +913,10 @@ enum {

TCA_FQ_TIMER_SLACK, /* timer slack */

TCA_FQ_HORIZON, /* time horizon in us */

TCA_FQ_HORIZON_DROP, /* drop packets beyond horizon, or cap their EDT */

__TCA_FQ_MAX
};

Expand All @@ -932,6 +936,8 @@ struct tc_fq_qd_stats {
__u32 throttled_flows;
__u32 unthrottle_latency_ns;
__u64 ce_mark; /* packets above ce_threshold */
__u64 horizon_drops;
__u64 horizon_caps;
};

/* Heavy-Hitter Filter */
Expand Down
59 changes: 54 additions & 5 deletions net/sched/sch_fq.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,7 @@ struct fq_sched_data {

struct rb_root delayed; /* for rate limited flows */
u64 time_next_delayed_flow;
u64 ktime_cache; /* copy of last ktime_get_ns() */
unsigned long unthrottle_latency_ns;

struct fq_flow internal; /* for non classified or high prio packets */
Expand All @@ -109,12 +110,13 @@ struct fq_sched_data {
u32 flow_plimit; /* max packets per flow */
unsigned long flow_max_rate; /* optional max rate per flow */
u64 ce_threshold;
u64 horizon; /* horizon in ns */
u32 orphan_mask; /* mask for orphaned skb */
u32 low_rate_threshold;
struct rb_root *fq_root;
u8 rate_enable;
u8 fq_trees_log;

u8 horizon_drop;
u32 flows;
u32 inactive_flows;
u32 throttled_flows;
Expand All @@ -123,6 +125,8 @@ struct fq_sched_data {
u64 stat_internal_packets;
u64 stat_throttled;
u64 stat_ce_mark;
u64 stat_horizon_drops;
u64 stat_horizon_caps;
u64 stat_flows_plimit;
u64 stat_pkts_too_long;
u64 stat_allocation_errors;
Expand Down Expand Up @@ -402,8 +406,6 @@ static void flow_queue_add(struct fq_flow *flow, struct sk_buff *skb)
struct rb_node **p, *parent;
struct sk_buff *head, *aux;

fq_skb_cb(skb)->time_to_send = skb->tstamp ?: ktime_get_ns();

head = flow->head;
if (!head ||
fq_skb_cb(skb)->time_to_send >= fq_skb_cb(flow->tail)->time_to_send) {
Expand Down Expand Up @@ -431,6 +433,12 @@ static void flow_queue_add(struct fq_flow *flow, struct sk_buff *skb)
rb_insert_color(&skb->rbnode, &flow->t_root);
}

static bool fq_packet_beyond_horizon(const struct sk_buff *skb,
const struct fq_sched_data *q)
{
return unlikely((s64)skb->tstamp > (s64)(q->ktime_cache + q->horizon));
}

static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
Expand All @@ -440,6 +448,28 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (unlikely(sch->q.qlen >= sch->limit))
return qdisc_drop(skb, sch, to_free);

if (!skb->tstamp) {
fq_skb_cb(skb)->time_to_send = q->ktime_cache = ktime_get_ns();
} else {
/* Check if packet timestamp is too far in the future.
* Try first if our cached value, to avoid ktime_get_ns()
* cost in most cases.
*/
if (fq_packet_beyond_horizon(skb, q)) {
/* Refresh our cache and check another time */
q->ktime_cache = ktime_get_ns();
if (fq_packet_beyond_horizon(skb, q)) {
if (q->horizon_drop) {
q->stat_horizon_drops++;
return qdisc_drop(skb, sch, to_free);
}
q->stat_horizon_caps++;
skb->tstamp = q->ktime_cache + q->horizon;
}
}
fq_skb_cb(skb)->time_to_send = skb->tstamp;
}

f = fq_classify(skb, q);
if (unlikely(f->qlen >= q->flow_plimit && f != &q->internal)) {
q->stat_flows_plimit++;
Expand Down Expand Up @@ -512,7 +542,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
goto out;
}

now = ktime_get_ns();
q->ktime_cache = now = ktime_get_ns();
fq_check_throttled(q, now);
begin:
head = &q->new_flows;
Expand Down Expand Up @@ -765,6 +795,8 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
[TCA_FQ_LOW_RATE_THRESHOLD] = { .type = NLA_U32 },
[TCA_FQ_CE_THRESHOLD] = { .type = NLA_U32 },
[TCA_FQ_TIMER_SLACK] = { .type = NLA_U32 },
[TCA_FQ_HORIZON] = { .type = NLA_U32 },
[TCA_FQ_HORIZON_DROP] = { .type = NLA_U8 },
};

static int fq_change(struct Qdisc *sch, struct nlattr *opt,
Expand Down Expand Up @@ -854,7 +886,15 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt,
if (tb[TCA_FQ_TIMER_SLACK])
q->timer_slack = nla_get_u32(tb[TCA_FQ_TIMER_SLACK]);

if (tb[TCA_FQ_HORIZON])
q->horizon = (u64)NSEC_PER_USEC *
nla_get_u32(tb[TCA_FQ_HORIZON]);

if (tb[TCA_FQ_HORIZON_DROP])
q->horizon_drop = nla_get_u8(tb[TCA_FQ_HORIZON_DROP]);

if (!err) {

sch_tree_unlock(sch);
err = fq_resize(sch, fq_log);
sch_tree_lock(sch);
Expand Down Expand Up @@ -907,6 +947,9 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt,

q->timer_slack = 10 * NSEC_PER_USEC; /* 10 usec of hrtimer slack */

q->horizon = 10ULL * NSEC_PER_SEC; /* 10 seconds */
q->horizon_drop = 1; /* by default, drop packets beyond horizon */

/* Default ce_threshold of 4294 seconds */
q->ce_threshold = (u64)NSEC_PER_USEC * ~0U;

Expand All @@ -924,6 +967,7 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
{
struct fq_sched_data *q = qdisc_priv(sch);
u64 ce_threshold = q->ce_threshold;
u64 horizon = q->horizon;
struct nlattr *opts;

opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
Expand All @@ -933,6 +977,7 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
/* TCA_FQ_FLOW_DEFAULT_RATE is not used anymore */

do_div(ce_threshold, NSEC_PER_USEC);
do_div(horizon, NSEC_PER_USEC);

if (nla_put_u32(skb, TCA_FQ_PLIMIT, sch->limit) ||
nla_put_u32(skb, TCA_FQ_FLOW_PLIMIT, q->flow_plimit) ||
Expand All @@ -948,7 +993,9 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
q->low_rate_threshold) ||
nla_put_u32(skb, TCA_FQ_CE_THRESHOLD, (u32)ce_threshold) ||
nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log) ||
nla_put_u32(skb, TCA_FQ_TIMER_SLACK, q->timer_slack))
nla_put_u32(skb, TCA_FQ_TIMER_SLACK, q->timer_slack) ||
nla_put_u32(skb, TCA_FQ_HORIZON, (u32)horizon) ||
nla_put_u8(skb, TCA_FQ_HORIZON_DROP, q->horizon_drop))
goto nla_put_failure;

return nla_nest_end(skb, opts);
Expand Down Expand Up @@ -979,6 +1026,8 @@ static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
st.unthrottle_latency_ns = min_t(unsigned long,
q->unthrottle_latency_ns, ~0U);
st.ce_mark = q->stat_ce_mark;
st.horizon_drops = q->stat_horizon_drops;
st.horizon_caps = q->stat_horizon_caps;
sch_tree_unlock(sch);

return gnet_stats_copy_app(d, &st, sizeof(st));
Expand Down

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