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net_sched: sch_fq: add 3 bands and WRR scheduling

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Before Google adopted FQ for its production servers,
we had to ensure AF4 packets would get a higher share
than BE1 ones.

As discussed this week in Netconf 2023 in Paris, it is time
to upstream this for public use.

After this patch FQ can replace pfifo_fast, with the following
differences :

- FQ uses WRR instead of strict prio, to avoid starvation of
  low priority packets.

- We make sure each band/prio tracks its own usage against sch->limit.
  This was done to make sure flood of low priority packets would not
  prevent AF4 packets to be queued. Contributed by Willem.

- priomap can be changed, if needed (default value are the ones
  coming from pfifo_fast).

In this patch, we set default band weights so that :

- high prio (band=0) packets get 90% of the bandwidth
  if they compete with low prio (band=2) packets.

- high prio packets get 75% of the bandwidth
  if they compete with medium prio (band=1) packets.

Following patch in this series adds the possibility to tune
the per-band weights.

As we added many fields in 'struct fq_sched_data', we had
to make sure to have the first cache line read-mostly, and
avoid wasting precious cache lines.

More optimizations are possible but will be sent separately.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Dave Taht <dave.taht@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2023-10-02 13:17:37 +00:00 committed by Paolo Abeni
parent 5579ee462d
commit 29f834aa32
2 changed files with 171 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/uapi/linux/pkt_sched.h
View File

@ -941,15 +941,19 @@ enum {
TCA_FQ_HORIZON_DROP, /* drop packets beyond horizon, or cap their EDT */
TCA_FQ_PRIOMAP, /* prio2band */
__TCA_FQ_MAX
};
#define TCA_FQ_MAX (__TCA_FQ_MAX - 1)
#define FQ_BANDS 3
struct tc_fq_qd_stats {
__u64 gc_flows;
__u64 highprio_packets;
__u64 tcp_retrans;
__u64 highprio_packets; /* obsolete */
__u64 tcp_retrans; /* obsolete */
__u64 throttled;
__u64 flows_plimit;
__u64 pkts_too_long;
@ -963,6 +967,9 @@ struct tc_fq_qd_stats {
__u64 horizon_drops;
__u64 horizon_caps;
__u64 fastpath_packets;
__u64 band_drops[FQ_BANDS];
__u32 band_pkt_count[FQ_BANDS];
__u32 pad;
};
/* Heavy-Hitter Filter */

204
net/sched/sch_fq.c
View File

@ -51,7 +51,8 @@
#include <net/tcp.h>
struct fq_skb_cb {
u64 time_to_send;
u64 time_to_send;
u8 band;
};
static inline struct fq_skb_cb *fq_skb_cb(struct sk_buff *skb)
@ -84,32 +85,28 @@ struct fq_flow {
u32 socket_hash; /* sk_hash */
int qlen; /* number of packets in flow queue */
/* Second cache line, used in fq_dequeue() */
/* Second cache line */
int credit;
/* 32bit hole on 64bit arches */
int band;
struct fq_flow *next; /* next pointer in RR lists */
struct rb_node rate_node; /* anchor in q->delayed tree */
u64 time_next_packet;
} ____cacheline_aligned_in_smp;
};
struct fq_flow_head {
struct fq_flow *first;
struct fq_flow *last;
};
struct fq_sched_data {
struct fq_perband_flows {
struct fq_flow_head new_flows;
struct fq_flow_head old_flows;
int credit;
int quantum; /* based on band nr : 576KB, 192KB, 64KB */
};
struct rb_root delayed; /* for rate limited flows */
u64 time_next_delayed_flow;
unsigned long unthrottle_latency_ns;
struct fq_flow internal; /* for non classified or high prio packets */
struct fq_sched_data {
/* Read mostly cache line */
u32 quantum;
@ -125,10 +122,21 @@ struct fq_sched_data {
u8 rate_enable;
u8 fq_trees_log;
u8 horizon_drop;
u8 prio2band[(TC_PRIO_MAX + 1) >> 2];
u32 timer_slack; /* hrtimer slack in ns */
/* Read/Write fields. */
unsigned int band_nr; /* band being serviced in fq_dequeue() */
struct fq_perband_flows band_flows[FQ_BANDS];
struct fq_flow internal; /* fastpath queue. */
struct rb_root delayed; /* for rate limited flows */
u64 time_next_delayed_flow;
unsigned long unthrottle_latency_ns;
u32 band_pkt_count[FQ_BANDS];
u32 flows;
u32 inactive_flows; /* Flows with no packet to send. */
u32 throttled_flows;
@ -139,7 +147,7 @@ struct fq_sched_data {
/* Seldom used fields. */
u64 stat_internal_packets; /* aka highprio */
u64 stat_band_drops[FQ_BANDS];
u64 stat_ce_mark;
u64 stat_horizon_drops;
u64 stat_horizon_caps;
@ -148,6 +156,12 @@ struct fq_sched_data {
u64 stat_allocation_errors;
};
/* return the i-th 2-bit value ("crumb") */
static u8 fq_prio2band(const u8 *prio2band, unsigned int prio)
{
return (prio2band[prio / 4] >> (2 * (prio & 0x3))) & 0x3;
}
/*
* f->tail and f->age share the same location.
* We can use the low order bit to differentiate if this location points
@ -172,8 +186,19 @@ static bool fq_flow_is_throttled(const struct fq_flow *f)
return f->next == &throttled;
}
static void fq_flow_add_tail(struct fq_flow_head *head, struct fq_flow *flow)
enum new_flow {
NEW_FLOW,
OLD_FLOW
};
static void fq_flow_add_tail(struct fq_sched_data *q, struct fq_flow *flow,
enum new_flow list_sel)
{
struct fq_perband_flows *pband = &q->band_flows[flow->band];
struct fq_flow_head *head = (list_sel == NEW_FLOW) ?
&pband->new_flows :
&pband->old_flows;
if (head->first)
head->last->next = flow;
else
@ -186,7 +211,7 @@ static void fq_flow_unset_throttled(struct fq_sched_data *q, struct fq_flow *f)
{
rb_erase(&f->rate_node, &q->delayed);
q->throttled_flows--;
fq_flow_add_tail(&q->old_flows, f);
fq_flow_add_tail(q, f, OLD_FLOW);
}
static void fq_flow_set_throttled(struct fq_sched_data *q, struct fq_flow *f)
@ -326,11 +351,6 @@ static struct fq_flow *fq_classify(struct Qdisc *sch, struct sk_buff *skb,
struct rb_root *root;
struct fq_flow *f;
/* warning: no starvation prevention... */
if (unlikely((skb->priority & TC_PRIO_MAX) == TC_PRIO_CONTROL)) {
q->stat_internal_packets++; /* highprio packet */
return &q->internal;
}
/* SYNACK messages are attached to a TCP_NEW_SYN_RECV request socket
* or a listener (SYNCOOKIE mode)
* 1) request sockets are not full blown,
@ -509,9 +529,13 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct fq_sched_data *q = qdisc_priv(sch);
struct fq_flow *f;
u64 now;
u8 band;
if (unlikely(sch->q.qlen >= sch->limit))
band = fq_prio2band(q->prio2band, skb->priority & TC_PRIO_MAX);
if (unlikely(q->band_pkt_count[band] >= sch->limit)) {
q->stat_band_drops[band]++;
return qdisc_drop(skb, sch, to_free);
}
now = ktime_get_ns();
if (!skb->tstamp) {
@ -538,11 +562,14 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
}
if (fq_flow_is_detached(f)) {
fq_flow_add_tail(&q->new_flows, f);
fq_flow_add_tail(q, f, NEW_FLOW);
if (time_after(jiffies, f->age + q->flow_refill_delay))
f->credit = max_t(u32, f->credit, q->quantum);
}
f->band = band;
q->band_pkt_count[band]++;
fq_skb_cb(skb)->band = band;
if (f->qlen == 0)
q->inactive_flows--;
}
@ -584,13 +611,26 @@ static void fq_check_throttled(struct fq_sched_data *q, u64 now)
}
}
static struct fq_flow_head *fq_pband_head_select(struct fq_perband_flows *pband)
{
if (pband->credit <= 0)
return NULL;
if (pband->new_flows.first)
return &pband->new_flows;
return pband->old_flows.first ? &pband->old_flows : NULL;
}
static struct sk_buff *fq_dequeue(struct Qdisc *sch)
{
struct fq_sched_data *q = qdisc_priv(sch);
struct fq_perband_flows *pband;
struct fq_flow_head *head;
struct sk_buff *skb;
struct fq_flow *f;
unsigned long rate;
int retry;
u32 plen;
u64 now;
@ -606,24 +646,31 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
now = ktime_get_ns();
fq_check_throttled(q, now);
retry = 0;
pband = &q->band_flows[q->band_nr];
begin:
head = &q->new_flows;
if (!head->first) {
head = &q->old_flows;
if (!head->first) {
if (q->time_next_delayed_flow != ~0ULL)
qdisc_watchdog_schedule_range_ns(&q->watchdog,
head = fq_pband_head_select(pband);
if (!head) {
while (++retry < FQ_BANDS) {
if (++q->band_nr == FQ_BANDS)
q->band_nr = 0;
pband = &q->band_flows[q->band_nr];
pband->credit = min(pband->credit + pband->quantum,
pband->quantum);
goto begin;
}
if (q->time_next_delayed_flow != ~0ULL)
qdisc_watchdog_schedule_range_ns(&q->watchdog,
q->time_next_delayed_flow,
q->timer_slack);
return NULL;
}
return NULL;
}
f = head->first;
retry = 0;
if (f->credit <= 0) {
f->credit += q->quantum;
head->first = f->next;
fq_flow_add_tail(&q->old_flows, f);
fq_flow_add_tail(q, f, OLD_FLOW);
goto begin;
}
@ -645,12 +692,13 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
}
if (--f->qlen == 0)
q->inactive_flows++;
q->band_pkt_count[fq_skb_cb(skb)->band]--;
fq_dequeue_skb(sch, f, skb);
} else {
head->first = f->next;
/* force a pass through old_flows to prevent starvation */
if ((head == &q->new_flows) && q->old_flows.first) {
fq_flow_add_tail(&q->old_flows, f);
if (head == &pband->new_flows) {
fq_flow_add_tail(q, f, OLD_FLOW);
} else {
fq_flow_set_detached(f);
}
@ -658,6 +706,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
}
plen = qdisc_pkt_len(skb);
f->credit -= plen;
pband->credit -= plen;
if (!q->rate_enable)
goto out;
@ -749,8 +798,10 @@ static void fq_reset(struct Qdisc *sch)
kmem_cache_free(fq_flow_cachep, f);
}
}
q->new_flows.first = NULL;
q->old_flows.first = NULL;
for (idx = 0; idx < FQ_BANDS; idx++) {
q->band_flows[idx].new_flows.first = NULL;
q->band_flows[idx].old_flows.first = NULL;
}
q->delayed = RB_ROOT;
q->flows = 0;
q->inactive_flows = 0;
@ -864,8 +915,54 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
[TCA_FQ_TIMER_SLACK] = { .type = NLA_U32 },
[TCA_FQ_HORIZON] = { .type = NLA_U32 },
[TCA_FQ_HORIZON_DROP] = { .type = NLA_U8 },
[TCA_FQ_PRIOMAP] = {
.type = NLA_BINARY,
.len = sizeof(struct tc_prio_qopt),
},
};
/* compress a u8 array with all elems <= 3 to an array of 2-bit fields */
static void fq_prio2band_compress_crumb(const u8 *in, u8 *out)
{
const int num_elems = TC_PRIO_MAX + 1;
int i;
memset(out, 0, num_elems / 4);
for (i = 0; i < num_elems; i++)
out[i / 4] |= in[i] << (2 * (i & 0x3));
}
static void fq_prio2band_decompress_crumb(const u8 *in, u8 *out)
{
const int num_elems = TC_PRIO_MAX + 1;
int i;
for (i = 0; i < num_elems; i++)
out[i] = fq_prio2band(in, i);
}
static int fq_load_priomap(struct fq_sched_data *q,
const struct nlattr *attr,
struct netlink_ext_ack *extack)
{
const struct tc_prio_qopt *map = nla_data(attr);
int i;
if (map->bands != FQ_BANDS) {
NL_SET_ERR_MSG_MOD(extack, "FQ only supports 3 bands");
return -EINVAL;
}
for (i = 0; i < TC_PRIO_MAX + 1; i++) {
if (map->priomap[i] >= FQ_BANDS) {
NL_SET_ERR_MSG_FMT_MOD(extack, "FQ priomap field %d maps to a too high band %d",
i, map->priomap[i]);
return -EINVAL;
}
}
fq_prio2band_compress_crumb(map->priomap, q->prio2band);
return 0;
}
static int fq_change(struct Qdisc *sch, struct nlattr *opt,
struct netlink_ext_ack *extack)
{
@ -940,6 +1037,9 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt,
q->flow_refill_delay = usecs_to_jiffies(usecs_delay);
}
if (!err && tb[TCA_FQ_PRIOMAP])
err = fq_load_priomap(q, tb[TCA_FQ_PRIOMAP], extack);
if (tb[TCA_FQ_ORPHAN_MASK])
q->orphan_mask = nla_get_u32(tb[TCA_FQ_ORPHAN_MASK]);
@ -991,7 +1091,7 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt,
struct netlink_ext_ack *extack)
{
struct fq_sched_data *q = qdisc_priv(sch);
int err;
int i, err;
sch->limit = 10000;
q->flow_plimit = 100;
@ -1001,8 +1101,13 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt,
q->flow_max_rate = ~0UL;
q->time_next_delayed_flow = ~0ULL;
q->rate_enable = 1;
q->new_flows.first = NULL;
q->old_flows.first = NULL;
for (i = 0; i < FQ_BANDS; i++) {
q->band_flows[i].new_flows.first = NULL;
q->band_flows[i].old_flows.first = NULL;
}
q->band_flows[0].quantum = 9 << 16;
q->band_flows[1].quantum = 3 << 16;
q->band_flows[2].quantum = 1 << 16;
q->delayed = RB_ROOT;
q->fq_root = NULL;
q->fq_trees_log = ilog2(1024);
@ -1017,6 +1122,7 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt,
/* Default ce_threshold of 4294 seconds */
q->ce_threshold = (u64)NSEC_PER_USEC * ~0U;
fq_prio2band_compress_crumb(sch_default_prio2band, q->prio2band);
qdisc_watchdog_init_clockid(&q->watchdog, sch, CLOCK_MONOTONIC);
if (opt)
@ -1031,6 +1137,9 @@ 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;
struct tc_prio_qopt prio = {
.bands = FQ_BANDS,
};
u64 horizon = q->horizon;
struct nlattr *opts;
@ -1062,6 +1171,10 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
nla_put_u8(skb, TCA_FQ_HORIZON_DROP, q->horizon_drop))
goto nla_put_failure;
fq_prio2band_decompress_crumb(q->prio2band, prio.priomap);
if (nla_put(skb, TCA_FQ_PRIOMAP, sizeof(prio), &prio))
goto nla_put_failure;
return nla_nest_end(skb, opts);
nla_put_failure:
@ -1072,11 +1185,14 @@ static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
struct fq_sched_data *q = qdisc_priv(sch);
struct tc_fq_qd_stats st;
int i;
st.pad = 0;
sch_tree_lock(sch);
st.gc_flows = q->stat_gc_flows;
st.highprio_packets = q->stat_internal_packets;
st.highprio_packets = 0;
st.fastpath_packets = q->internal.stat_fastpath_packets;
st.tcp_retrans = 0;
st.throttled = q->stat_throttled;
@ -1093,6 +1209,10 @@ static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
st.ce_mark = q->stat_ce_mark;
st.horizon_drops = q->stat_horizon_drops;
st.horizon_caps = q->stat_horizon_caps;
for (i = 0; i < FQ_BANDS; i++) {
st.band_drops[i] = q->stat_band_drops[i];
st.band_pkt_count[i] = q->band_pkt_count[i];
}
sch_tree_unlock(sch);
return gnet_stats_copy_app(d, &st, sizeof(st));
@ -1120,7 +1240,7 @@ static int __init fq_module_init(void)
fq_flow_cachep = kmem_cache_create("fq_flow_cache",
sizeof(struct fq_flow),
0, 0, NULL);
0, SLAB_HWCACHE_ALIGN, NULL);
if (!fq_flow_cachep)
return -ENOMEM;