From: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com
DualPI2 is the reference implementation of IETF RFC9332 DualQ Coupled AQM (https://datatracker.ietf.org/doc/html/rfc9332) providing two queues called low latency (L-queue) and classic (C-queue). By default, it enqueues non-ECN and ECT(0) packets into the C-queue and ECT(1) and CE packets into the low latency queue (L-queue), as per IETF RFC9332 spec.
This patch defines the dualpi2 Qdisc structure and parsing, and the following two patches include dumping and enqueue/dequeue for the DualPI2.
Signed-off-by: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com --- include/uapi/linux/pkt_sched.h | 24 ++ net/sched/sch_dualpi2.c | 554 +++++++++++++++++++++++++++++++++ 2 files changed, 578 insertions(+) create mode 100644 net/sched/sch_dualpi2.c
diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h index 9ea874395717..b4caeccbea72 100644 --- a/include/uapi/linux/pkt_sched.h +++ b/include/uapi/linux/pkt_sched.h @@ -1210,4 +1210,28 @@ enum {
#define TCA_ETS_MAX (__TCA_ETS_MAX - 1)
+/* DUALPI2 */ +enum { + TCA_DUALPI2_UNSPEC, + TCA_DUALPI2_LIMIT, /* Packets */ + TCA_DUALPI2_MEMORY_LIMIT, /* Bytes */ + TCA_DUALPI2_TARGET, /* us */ + TCA_DUALPI2_TUPDATE, /* us */ + TCA_DUALPI2_ALPHA, /* Hz scaled up by 256 */ + TCA_DUALPI2_BETA, /* HZ scaled up by 256 */ + TCA_DUALPI2_STEP_THRESH, /* Packets or us */ + TCA_DUALPI2_STEP_PACKETS, /* Whether STEP_THRESH is in packets */ + TCA_DUALPI2_MIN_QLEN_STEP, /* Minimum qlen to apply STEP_THRESH */ + TCA_DUALPI2_COUPLING, /* Coupling factor between queues */ + TCA_DUALPI2_DROP_OVERLOAD, /* Whether to drop on overload */ + TCA_DUALPI2_DROP_EARLY, /* Whether to drop on enqueue */ + TCA_DUALPI2_C_PROTECTION, /* Percentage */ + TCA_DUALPI2_ECN_MASK, /* L4S queue classification mask */ + TCA_DUALPI2_SPLIT_GSO, /* Split GSO packets at enqueue */ + TCA_DUALPI2_PAD, + __TCA_DUALPI2_MAX +}; + +#define TCA_DUALPI2_MAX (__TCA_DUALPI2_MAX - 1) + #endif diff --git a/net/sched/sch_dualpi2.c b/net/sched/sch_dualpi2.c new file mode 100644 index 000000000000..bb3d9982b572 --- /dev/null +++ b/net/sched/sch_dualpi2.c @@ -0,0 +1,554 @@ +// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause +/* Copyright (C) 2024 Nokia + * + * Author: Koen De Schepper koen.de_schepper@nokia-bell-labs.com + * Author: Olga Albisser olga@albisser.org + * Author: Henrik Steen henrist@henrist.net + * Author: Olivier Tilmans olivier.tilmans@nokia.com + * Author: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com + * + * DualPI Improved with a Square (dualpi2): + * - Supports congestion controls that comply with the Prague requirements + * in RFC9331 (e.g. TCP-Prague) + * - Supports coupled dual-queue with PI2 as defined in RFC9332 + * - Supports ECN L4S-identifier (IP.ECN==0b*1) + * + * note: Although DCTCP and BBRv3 can use shallow-threshold ECN marks, + * they do not meet the 'Prague L4S Requirements' listed in RFC 9331 + * Section 4, so they can only be used with DualPI2 in a datacenter + * context. + * + * References: + * - RFC9332: https://datatracker.ietf.org/doc/html/rfc9332 + * - De Schepper, Koen, et al. "PI 2: A linearized AQM for both classic and + * scalable TCP." in proc. ACM CoNEXT'16, 2016. + */ + +#include <linux/errno.h> +#include <linux/hrtimer.h> +#include <linux/if_vlan.h> +#include <linux/kernel.h> +#include <linux/limits.h> +#include <linux/module.h> +#include <linux/skbuff.h> +#include <linux/types.h> + +#include <net/gso.h> +#include <net/inet_ecn.h> +#include <net/pkt_cls.h> +#include <net/pkt_sched.h> + +/* 32b enable to support flows with windows up to ~8.6 * 1e9 packets + * i.e., twice the maximal snd_cwnd. + * MAX_PROB must be consistent with the RNG in dualpi2_roll(). + */ +#define MAX_PROB U32_MAX + +/* alpha/beta values exchanged over netlink are in units of 256ns */ +#define ALPHA_BETA_SHIFT 8 + +/* Scaled values of alpha/beta must fit in 32b to avoid overflow in later + * computations. Consequently (see and dualpi2_scale_alpha_beta()), their + * netlink-provided values can use at most 31b, i.e. be at most (2^23)-1 + * (~4MHz) as those are given in 1/256th. This enable to tune alpha/beta to + * control flows whose maximal RTTs can be in usec up to few secs. + */ +#define ALPHA_BETA_MAX ((1U << 31) - 1) + +/* Internal alpha/beta are in units of 64ns. + * This enables to use all alpha/beta values in the allowed range without loss + * of precision due to rounding when scaling them internally, e.g., + * scale_alpha_beta(1) will not round down to 0. + */ +#define ALPHA_BETA_GRANULARITY 6 + +#define ALPHA_BETA_SCALING (ALPHA_BETA_SHIFT - ALPHA_BETA_GRANULARITY) + +/* We express the weights (wc, wl) in %, i.e., wc + wl = 100 */ +#define MAX_WC 100 + +struct dualpi2_sched_data { + struct Qdisc *l_queue; /* The L4S Low latency queue (L-queue) */ + struct Qdisc *sch; /* The Classic queue (C-queue) */ + + /* Registered tc filters */ + struct tcf_proto __rcu *tcf_filters; + struct tcf_block *tcf_block; + + /* PI2 parameters */ + u64 pi2_target; /* Target delay in nanoseconds */ + u32 pi2_tupdate; /* Timer frequency in nanoseconds */ + u32 pi2_prob; /* Base PI probability */ + u32 pi2_alpha; /* Gain factor for the integral rate response */ + u32 pi2_beta; /* Gain factor for the proportional response */ + struct hrtimer pi2_timer; /* prob update timer */ + + /* Step AQM (L-queue only) parameters */ + u32 step_thresh; /* Step threshold */ + bool step_in_packets; /* Whether the step is in packets or time */ + + /* C-queue starvation protection */ + s32 c_protection_credit; /* Credit (sign indicates which queue) */ + s32 c_protection_init; /* Reset value of the credit */ + u8 c_protection_wc; /* C-queue weight (between 0 and MAX_WC) */ + u8 c_protection_wl; /* L-queue weight (MAX_WC - wc) */ + + /* General dualQ parameters */ + u32 memory_limit; /* Memory limit of both queues */ + u8 coupling_factor;/* Coupling factor (k) between both queues */ + u8 ecn_mask; /* Mask to match packets into L-queue */ + u32 min_qlen_step; /* Minimum queue length to apply step thresh */ + bool drop_early; /* Drop at enqueue instead of dequeue if true */ + bool drop_overload; /* Drop (1) on overload, or overflow (0) */ + bool split_gso; /* Split aggregated skb (1) or leave as is */ + + /* Statistics */ + u64 c_head_ts; /* Enqueue timestamp of the C-queue head */ + u64 l_head_ts; /* Enqueue timestamp of the L-queue head */ + u64 last_qdelay; /* Q delay val at the last probability update */ + u32 packets_in_c; /* Enqueue packet counter of the C-queue */ + u32 packets_in_l; /* Enqueue packet counter of the L-queue */ + u32 maxq; /* Maximum queue size of the C-queue */ + u32 ecn_mark; /* ECN mark pkt counter due to PI probability */ + u32 step_marks; /* ECN mark pkt counter due to step AQM */ + u32 memory_used; /* Memory used of both queues */ + u32 max_memory_used;/* Maximum used memory */ +}; + +static u32 dualpi2_scale_alpha_beta(u32 param) +{ + u64 tmp = ((u64)param * MAX_PROB >> ALPHA_BETA_SCALING); + + do_div(tmp, NSEC_PER_SEC); + return tmp; +} + +static ktime_t next_pi2_timeout(struct dualpi2_sched_data *q) +{ + return ktime_add_ns(ktime_get_ns(), q->pi2_tupdate); +} + +static void dualpi2_reset_c_protection(struct dualpi2_sched_data *q) +{ + q->c_protection_credit = q->c_protection_init; +} + +/* This computes the initial credit value and WRR weight for the L queue (wl) + * from the weight of the C queue (wc). + * If wl > wc, the scheduler will start with the L queue when reset. + */ +static void dualpi2_calculate_c_protection(struct Qdisc *sch, + struct dualpi2_sched_data *q, u32 wc) +{ + q->c_protection_wc = wc; + q->c_protection_wl = MAX_WC - wc; + q->c_protection_init = (s32)psched_mtu(qdisc_dev(sch)) * + ((int)q->c_protection_wc - (int)q->c_protection_wl); + dualpi2_reset_c_protection(q); +} + +static s64 __scale_delta(u64 diff) +{ + do_div(diff, 1 << ALPHA_BETA_GRANULARITY); + return diff; +} + +static void get_queue_delays(struct dualpi2_sched_data *q, u64 *qdelay_c, + u64 *qdelay_l) +{ + u64 now, qc, ql; + + now = ktime_get_ns(); + qc = READ_ONCE(q->c_head_ts); + ql = READ_ONCE(q->l_head_ts); + + *qdelay_c = qc ? now - qc : 0; + *qdelay_l = ql ? now - ql : 0; +} + +static u32 calculate_probability(struct Qdisc *sch) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + u32 new_prob; + u64 qdelay_c; + u64 qdelay_l; + u64 qdelay; + s64 delta; + + get_queue_delays(q, &qdelay_c, &qdelay_l); + qdelay = max(qdelay_l, qdelay_c); + /* Alpha and beta take at most 32b, i.e, the delay difference would + * overflow for queuing delay differences > ~4.2sec. + */ + delta = ((s64)qdelay - q->pi2_target) * q->pi2_alpha; + delta += ((s64)qdelay - q->last_qdelay) * q->pi2_beta; + if (delta > 0) { + new_prob = __scale_delta(delta) + q->pi2_prob; + if (new_prob < q->pi2_prob) + new_prob = MAX_PROB; + } else { + new_prob = q->pi2_prob - __scale_delta(~delta + 1); + if (new_prob > q->pi2_prob) + new_prob = 0; + } + q->last_qdelay = qdelay; + /* If we do not drop on overload, ensure we cap the L4S probability to + * 100% to keep window fairness when overflowing. + */ + if (!q->drop_overload) + return min_t(u32, new_prob, MAX_PROB / q->coupling_factor); + return new_prob; +} + +static u32 get_memory_limit(struct Qdisc *sch, u32 limit) +{ + /* Apply rule of thumb, i.e., doubling the packet length, + * to further include per packet overhead in memory_limit. + */ + u64 memlim = mul_u32_u32(limit, 2 * psched_mtu(qdisc_dev(sch))); + + if (upper_32_bits(memlim)) + return 0xffffffff; + else + return lower_32_bits(memlim); +} + +static enum hrtimer_restart dualpi2_timer(struct hrtimer *timer) +{ + struct dualpi2_sched_data *q = from_timer(q, timer, pi2_timer); + + WRITE_ONCE(q->pi2_prob, calculate_probability(q->sch)); + + hrtimer_set_expires(&q->pi2_timer, next_pi2_timeout(q)); + return HRTIMER_RESTART; +} + +static struct netlink_range_validation dualpi2_alpha_beta_range = { + .min = 1, + .max = ALPHA_BETA_MAX, +}; + +static struct netlink_range_validation dualpi2_wc_range = { + .min = 0, + .max = MAX_WC, +}; + +static const struct nla_policy dualpi2_policy[TCA_DUALPI2_MAX + 1] = { + [TCA_DUALPI2_LIMIT] = NLA_POLICY_MIN(NLA_U32, 1), + [TCA_DUALPI2_MEMORY_LIMIT] = NLA_POLICY_MIN(NLA_U32, 1), + [TCA_DUALPI2_TARGET] = {.type = NLA_U32}, + [TCA_DUALPI2_TUPDATE] = NLA_POLICY_MIN(NLA_U32, 1), + [TCA_DUALPI2_ALPHA] = + NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range), + [TCA_DUALPI2_BETA] = + NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range), + [TCA_DUALPI2_STEP_THRESH] = {.type = NLA_U32}, + [TCA_DUALPI2_STEP_PACKETS] = {.type = NLA_FLAG}, + [TCA_DUALPI2_MIN_QLEN_STEP] = {.type = NLA_U32}, + [TCA_DUALPI2_COUPLING] = NLA_POLICY_MIN(NLA_U8, 1), + [TCA_DUALPI2_DROP_OVERLOAD] = {.type = NLA_U8}, + [TCA_DUALPI2_DROP_EARLY] = {.type = NLA_U8}, + [TCA_DUALPI2_C_PROTECTION] = + NLA_POLICY_FULL_RANGE(NLA_U8, &dualpi2_wc_range), + [TCA_DUALPI2_ECN_MASK] = {.type = NLA_U8}, + [TCA_DUALPI2_SPLIT_GSO] = {.type = NLA_U8}, +}; + +static int dualpi2_change(struct Qdisc *sch, struct nlattr *opt, + struct netlink_ext_ack *extack) +{ + struct nlattr *tb[TCA_DUALPI2_MAX + 1]; + struct dualpi2_sched_data *q; + int old_backlog; + int old_qlen; + int err; + + if (!opt) + return -EINVAL; + err = nla_parse_nested(tb, TCA_DUALPI2_MAX, opt, dualpi2_policy, + extack); + if (err < 0) + return err; + + q = qdisc_priv(sch); + sch_tree_lock(sch); + + if (tb[TCA_DUALPI2_LIMIT]) { + u32 limit = nla_get_u32(tb[TCA_DUALPI2_LIMIT]); + + WRITE_ONCE(sch->limit, limit); + WRITE_ONCE(q->memory_limit, get_memory_limit(sch, limit)); + } + + if (tb[TCA_DUALPI2_MEMORY_LIMIT]) + WRITE_ONCE(q->memory_limit, + nla_get_u32(tb[TCA_DUALPI2_MEMORY_LIMIT])); + + if (tb[TCA_DUALPI2_TARGET]) { + u64 target = nla_get_u32(tb[TCA_DUALPI2_TARGET]); + + WRITE_ONCE(q->pi2_target, target * NSEC_PER_USEC); + } + + if (tb[TCA_DUALPI2_TUPDATE]) { + u64 tupdate = nla_get_u32(tb[TCA_DUALPI2_TUPDATE]); + + WRITE_ONCE(q->pi2_tupdate, tupdate * NSEC_PER_USEC); + } + + if (tb[TCA_DUALPI2_ALPHA]) { + u32 alpha = nla_get_u32(tb[TCA_DUALPI2_ALPHA]); + + WRITE_ONCE(q->pi2_alpha, dualpi2_scale_alpha_beta(alpha)); + } + + if (tb[TCA_DUALPI2_BETA]) { + u32 beta = nla_get_u32(tb[TCA_DUALPI2_BETA]); + + WRITE_ONCE(q->pi2_beta, dualpi2_scale_alpha_beta(beta)); + } + + if (tb[TCA_DUALPI2_STEP_THRESH]) { + u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH]); + bool step_pkt = nla_get_flag(tb[TCA_DUALPI2_STEP_PACKETS]); + + WRITE_ONCE(q->step_in_packets, step_pkt); + WRITE_ONCE(q->step_thresh, + step_pkt ? step_th : (step_th * NSEC_PER_USEC)); + } + + if (tb[TCA_DUALPI2_MIN_QLEN_STEP]) + WRITE_ONCE(q->min_qlen_step, + nla_get_u32(tb[TCA_DUALPI2_MIN_QLEN_STEP])); + + if (tb[TCA_DUALPI2_COUPLING]) { + u8 coupling = nla_get_u8(tb[TCA_DUALPI2_COUPLING]); + + WRITE_ONCE(q->coupling_factor, coupling); + } + + if (tb[TCA_DUALPI2_DROP_OVERLOAD]) + WRITE_ONCE(q->drop_overload, + !!nla_get_u8(tb[TCA_DUALPI2_DROP_OVERLOAD])); + + if (tb[TCA_DUALPI2_DROP_EARLY]) + WRITE_ONCE(q->drop_early, + !!nla_get_u8(tb[TCA_DUALPI2_DROP_EARLY])); + + if (tb[TCA_DUALPI2_C_PROTECTION]) { + u8 wc = nla_get_u8(tb[TCA_DUALPI2_C_PROTECTION]); + + dualpi2_calculate_c_protection(sch, q, wc); + } + + if (tb[TCA_DUALPI2_ECN_MASK]) + WRITE_ONCE(q->ecn_mask, + nla_get_u8(tb[TCA_DUALPI2_ECN_MASK])); + + if (tb[TCA_DUALPI2_SPLIT_GSO]) + WRITE_ONCE(q->split_gso, + !!nla_get_u8(tb[TCA_DUALPI2_SPLIT_GSO])); + + old_qlen = qdisc_qlen(sch); + old_backlog = sch->qstats.backlog; + while (qdisc_qlen(sch) > sch->limit || + q->memory_used > q->memory_limit) { + struct sk_buff *skb = __qdisc_dequeue_head(&sch->q); + + q->memory_used -= skb->truesize; + qdisc_qstats_backlog_dec(sch, skb); + rtnl_qdisc_drop(skb, sch); + } + qdisc_tree_reduce_backlog(sch, old_qlen - qdisc_qlen(sch), + old_backlog - sch->qstats.backlog); + + sch_tree_unlock(sch); + return 0; +} + +/* Default alpha/beta values give a 10dB stability margin with max_rtt=100ms. */ +static void dualpi2_reset_default(struct Qdisc *sch) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + + q->sch->limit = 10000; /* Max 125ms at 1Gbps */ + q->memory_limit = get_memory_limit(sch, q->sch->limit); + + q->pi2_target = 15 * NSEC_PER_MSEC; + q->pi2_tupdate = 16 * NSEC_PER_MSEC; + q->pi2_alpha = dualpi2_scale_alpha_beta(41); /* ~0.16 Hz * 256 */ + q->pi2_beta = dualpi2_scale_alpha_beta(819); /* ~3.20 Hz * 256 */ + + q->step_thresh = 1 * NSEC_PER_MSEC; + q->step_in_packets = false; + + dualpi2_calculate_c_protection(q->sch, q, 10); /* wc=10%, wl=90% */ + + q->ecn_mask = INET_ECN_ECT_1; + q->min_qlen_step = 0; + q->coupling_factor = 2; /* window fairness for equal RTTs */ + q->drop_overload = true; /* Preserve latency by dropping */ + q->drop_early = false; /* PI2 drops on dequeue */ + q->split_gso = true; +} + +static int dualpi2_init(struct Qdisc *sch, struct nlattr *opt, + struct netlink_ext_ack *extack) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + int err; + + q->l_queue = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops, + TC_H_MAKE(sch->handle, 1), extack); + if (!q->l_queue) + return -ENOMEM; + + err = tcf_block_get(&q->tcf_block, &q->tcf_filters, sch, extack); + if (err) + return err; + + q->sch = sch; + dualpi2_reset_default(sch); + hrtimer_setup(&q->pi2_timer, dualpi2_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED); + + if (opt) { + err = dualpi2_change(sch, opt, extack); + + if (err) + return err; + } + + hrtimer_start(&q->pi2_timer, next_pi2_timeout(q), + HRTIMER_MODE_ABS_PINNED); + return 0; +} + +/* Reset both L-queue and C-queue, internal packet counters, PI probability, + * C-queue protection credit, and timestamps, while preserving current + * configuration of DUALPI2. + */ +static void dualpi2_reset(struct Qdisc *sch) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + + qdisc_reset_queue(sch); + qdisc_reset_queue(q->l_queue); + q->c_head_ts = 0; + q->l_head_ts = 0; + q->pi2_prob = 0; + q->packets_in_c = 0; + q->packets_in_l = 0; + q->maxq = 0; + q->ecn_mark = 0; + q->step_marks = 0; + q->memory_used = 0; + q->max_memory_used = 0; + dualpi2_reset_c_protection(q); +} + +static void dualpi2_destroy(struct Qdisc *sch) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + + q->pi2_tupdate = 0; + hrtimer_cancel(&q->pi2_timer); + if (q->l_queue) + qdisc_put(q->l_queue); + tcf_block_put(q->tcf_block); +} + +static struct Qdisc *dualpi2_leaf(struct Qdisc *sch, unsigned long arg) +{ + return NULL; +} + +static unsigned long dualpi2_find(struct Qdisc *sch, u32 classid) +{ + return 0; +} + +static unsigned long dualpi2_bind(struct Qdisc *sch, unsigned long parent, + u32 classid) +{ + return 0; +} + +static void dualpi2_unbind(struct Qdisc *q, unsigned long cl) +{ +} + +static struct tcf_block *dualpi2_tcf_block(struct Qdisc *sch, unsigned long cl, + struct netlink_ext_ack *extack) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + + if (cl) + return NULL; + return q->tcf_block; +} + +static void dualpi2_walk(struct Qdisc *sch, struct qdisc_walker *arg) +{ + unsigned int i; + + if (arg->stop) + return; + + /* We statically define only 2 queues */ + for (i = 0; i < 2; i++) { + if (arg->count < arg->skip) { + arg->count++; + continue; + } + if (arg->fn(sch, i + 1, arg) < 0) { + arg->stop = 1; + break; + } + arg->count++; + } +} + +/* Minimal class support to handler tc filters */ +static const struct Qdisc_class_ops dualpi2_class_ops = { + .leaf = dualpi2_leaf, + .find = dualpi2_find, + .tcf_block = dualpi2_tcf_block, + .bind_tcf = dualpi2_bind, + .unbind_tcf = dualpi2_unbind, + .walk = dualpi2_walk, +}; + +static struct Qdisc_ops dualpi2_qdisc_ops __read_mostly = { + .id = "dualpi2", + .cl_ops = &dualpi2_class_ops, + .priv_size = sizeof(struct dualpi2_sched_data), + .peek = qdisc_peek_dequeued, + .init = dualpi2_init, + .destroy = dualpi2_destroy, + .reset = dualpi2_reset, + .change = dualpi2_change, + .owner = THIS_MODULE, +}; + +static int __init dualpi2_module_init(void) +{ + return register_qdisc(&dualpi2_qdisc_ops); +} + +static void __exit dualpi2_module_exit(void) +{ + unregister_qdisc(&dualpi2_qdisc_ops); +} + +module_init(dualpi2_module_init); +module_exit(dualpi2_module_exit); + +MODULE_DESCRIPTION("Dual Queue with Proportional Integral controller Improved with a Square (dualpi2) scheduler"); +MODULE_AUTHOR("Koen De Schepper koen.de_schepper@nokia-bell-labs.com"); +MODULE_AUTHOR("Olga Albisser olga@albisser.org"); +MODULE_AUTHOR("Henrik Steen henrist@henrist.net"); +MODULE_AUTHOR("Olivier Tilmans olivier.tilmans@nokia.com"); +MODULE_AUTHOR("Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com"); + +MODULE_LICENSE("Dual BSD/GPL"); +MODULE_VERSION("1.0");